feat: Add comprehensive PHPUnit test suite and CI/CD test gating (v0.5.0)

189 tests across 8 test classes covering all core plugin classes:
CustomMetricBuilder, StorageFactory, Authentication, DashboardProvider,
RuntimeCollector, Installer, Collector, and MetricsEndpoint.

Added test job to Gitea release workflow that gates build-release.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitea/workflows/release.yml

@@ -6,7 +6,7 @@ on:
       - 'v*'
 
 jobs:
-  build-release:
+  test:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
@@ -18,7 +18,32 @@ jobs:
         uses: shivammathur/setup-php@v2
         with:
           php-version: '8.3'
-          extensions: mbstring, xml, zip, intl, gettext
+          extensions: mbstring, xml, zip, intl, gettext, redis, apcu
+          tools: composer:v2
+
+      - name: Validate composer.json
+        run: composer validate --strict
+
+      - name: Install Composer dependencies
+        run: composer install --optimize-autoloader --no-interaction
+
+      - name: Run tests
+        run: composer test
+
+  build-release:
+    needs: test
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+        with:
+          submodules: recursive
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '8.3'
+          extensions: mbstring, xml, zip, intl, gettext, redis, apcu
           tools: composer:v2
 
       - name: Get version from tag

.gitignore

@@ -4,3 +4,9 @@ wp-plugins
 wp-core
 vendor/
 releases/*
+
+# Marketing texts (not for distribution)
+MARKETING.md
+
+# PHPUnit cache
+.phpunit.cache

CHANGELOG.md

@@ -5,6 +5,251 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.5.0] - 2026-02-26
+
+### Added
+
+- Comprehensive PHPUnit test suite with 189 tests and 329 assertions:
+  - CustomMetricBuilderTest (35 tests) - validation, CRUD, import/export
+  - AuthenticationTest (13 tests) - Bearer token, query param, header extraction
+  - StorageFactoryTest (25 tests) - adapter config, env vars, connection testing
+  - RuntimeCollectorTest (22 tests) - endpoint normalization, histograms, singleton
+  - DashboardProviderTest (27 tests) - registration validation, path traversal security
+  - InstallerTest (11 tests) - activation, deactivation, uninstall cleanup
+  - CollectorTest (10 tests) - registry, metric registration, render output
+  - MetricsEndpointTest (5 tests) - rewrite rules, request routing
+- Test bootstrap with WordPress function stubs and GlobalFunctionState helper
+- CI/CD test job in Gitea release workflow that gates release builds
+- php-mock/php-mock-phpunit dependency for mocking WordPress functions in namespaced code
+
+### Changed
+
+- Release pipeline now requires passing tests before building release packages
+
+## [0.4.9] - 2026-02-26
+
+### Security
+
+- Fixed XSS vulnerability: replaced all jQuery `.html()` injections with safe `.text()` DOM construction in admin.js
+- Fixed insecure token generation: replaced `Math.random()` with `crypto.getRandomValues()` (Web Crypto API)
+- Fixed XSS via string interpolation in `updateValueRows()`: replaced HTML string building with jQuery DOM construction
+- Added 1 MB import size limit to prevent DoS via large JSON payloads in CustomMetricBuilder
+- Removed `site_url` from metric export data to prevent information disclosure
+- Added import mode validation (allowlist check) in CustomMetricBuilder
+
+### Changed
+
+- Extracted shared authentication logic (`wp_prometheus_authenticate_request()`) to eliminate code duplication between MetricsEndpoint and isolated mode handler
+- Extracted `showNotice()` helper in admin.js to DRY up 10+ duplicated AJAX response handling patterns
+- Extracted `is_hpos_enabled()` helper method in Collector to DRY up WooCommerce HPOS checks
+- Optimized WooCommerce product type counting: uses `paginate: true` COUNT query instead of loading all product IDs into memory
+- Added missing options to `Installer::uninstall()` cleanup (isolated_mode, storage adapter, Redis/APCu config)
+
+## [0.4.8] - 2026-02-07
+
+### Fixed
+
+- Fixed `_load_textdomain_just_in_time` notice on admin pages (WordPress 6.7+ compatibility)
+- Deferred `load_plugin_textdomain()` to `init` action instead of `plugins_loaded`
+- Deferred Settings tab label and DashboardProvider initialization to avoid early translation loading
+
+## [0.4.7] - 2026-02-03
+
+### Added
+
+- Database query duration distribution panel in Grafana Runtime dashboard
+- `wordpress_db_query_duration_seconds` metric now listed in Help tab
+- Documentation for enabling `SAVEQUERIES` constant for query timing
+
+### Changed
+
+- Updated README with instructions for enabling database query timing
+- Grafana Runtime dashboard now includes bucket distribution chart for DB queries
+
+## [0.4.6] - 2026-02-03
+
+### Added
+
+- Dashboard extension hook `wp_prometheus_register_dashboards` for third-party plugins
+- Third-party plugins can now register their own Grafana dashboard templates
+- Support for file-based and inline JSON dashboard registration
+- "Extension" badge for third-party dashboards in admin UI
+- Plugin attribution display for third-party dashboards
+- Security: Path traversal protection for registered dashboard files
+- Isolated mode support for dashboard registration hook
+
+### Changed
+
+- DashboardProvider now supports both built-in and third-party registered dashboards
+- Dashboard cards show source (built-in vs extension) with visual distinction
+
+## [0.4.5] - 2026-02-02
+
+### Fixed
+
+- Settings now persist correctly across Metrics sub-tabs
+- Auth token no longer gets cleared when saving from Selection sub-tab
+- Enabled metrics no longer get cleared when saving from Endpoint sub-tab
+- Isolated mode setting no longer gets cleared when saving from other sub-tabs
+
+### Changed
+
+- Split Metrics settings into separate WordPress option groups per sub-tab
+- Each sub-tab now uses its own settings group to prevent cross-tab overwrites
+
+## [0.4.4] - 2026-02-02
+
+### Added
+
+- Safe mode for metrics collection (default):
+  - Removes problematic content filters early
+  - Allows third-party plugins to register `wp_prometheus_collect_metrics` hooks
+  - Wraps custom hooks in output buffering and try-catch for protection
+- Isolated mode option for maximum compatibility:
+  - Outputs metrics before other plugins fully load
+  - Use only if Safe mode causes issues
+- `WP_PROMETHEUS_ISOLATED_MODE` environment variable support
+- Mode comparison table in admin settings
+
+### Changed
+
+- Replaced "early mode" with two clear modes: Safe (default) and Isolated
+- Custom metrics hooks now fire by default with protection against recursion
+- Filter removal now also includes `the_content_feed` and `comment_text`
+- Updated admin UI with clearer explanations of each mode
+
+### Fixed
+
+- Third-party plugins can now add custom metrics without memory issues
+- Twig-based plugins (like wp-fedistream) no longer cause recursion
+
+## [0.4.3] - 2026-02-02
+
+### Added
+
+- Sub-tabs navigation within Metrics tab (Endpoint, Selection, Runtime, Advanced)
+- Option to disable early mode in admin settings (Metrics → Advanced)
+- Support for `WP_PROMETHEUS_DISABLE_EARLY_MODE` environment variable
+- Early mode status display in settings
+
+### Fixed
+
+- Early mode setting now saves correctly (moved into form with proper settings group)
+
+### Changed
+
+- Reorganized Metrics tab into logical sub-sections for better usability
+- Early mode can now be disabled for users who need the `wp_prometheus_collect_metrics` hook
+- Updated translations with sub-tab and early mode strings (English and German)
+
+## [0.4.1] - 2026-02-02
+
+### Fixed
+
+- Fixed memory exhaustion when wp-fedistream (Twig-based) plugin is active
+- Added early metrics endpoint handler that intercepts `/metrics` requests before full WordPress initialization
+- Removed content filters (`the_content`, `the_excerpt`, `get_the_excerpt`, `the_title`) during metrics collection to prevent recursion
+- Skip third-party extensibility hooks during early metrics mode to avoid conflicts
+- Changed `template_redirect` hook to `parse_request` for earlier request interception
+
+## [0.4.0] - 2026-02-02
+
+### Added
+
+- Persistent Storage Support:
+  - Redis storage adapter for shared metrics across multiple instances
+  - APCu storage adapter for single-server high-performance caching
+  - StorageFactory class for automatic adapter selection and fallback
+  - Connection testing with detailed error messages
+- New "Storage" tab in admin settings:
+  - Storage adapter selection (In-Memory, Redis, APCu)
+  - Redis configuration (host, port, password, database, key prefix)
+  - APCu configuration (key prefix)
+  - Connection test button
+  - Environment variables documentation
+- Environment variable configuration for Docker/containerized environments:
+  - `WP_PROMETHEUS_STORAGE_ADAPTER` - Select storage adapter
+  - `WP_PROMETHEUS_REDIS_HOST` - Redis server hostname
+  - `WP_PROMETHEUS_REDIS_PORT` - Redis server port
+  - `WP_PROMETHEUS_REDIS_PASSWORD` - Redis authentication
+  - `WP_PROMETHEUS_REDIS_DATABASE` - Redis database index (0-15)
+  - `WP_PROMETHEUS_REDIS_PREFIX` - Redis key prefix
+  - `WP_PROMETHEUS_APCU_PREFIX` - APCu key prefix
+- Automatic fallback to In-Memory storage if configured adapter fails
+- Docker Compose example in admin settings
+
+### Changed
+
+- Settings page now has 6 tabs: License, Metrics, Storage, Custom Metrics, Dashboards, Help
+- Updated translations with all new strings (English and German)
+- Collector now uses StorageFactory for storage adapter instantiation
+
+## [0.3.0] - 2026-02-02
+
+### Added
+
+- Custom Metrics Builder:
+  - Admin UI to define custom gauge metrics
+  - Support for static values and WordPress option-based values
+  - Label support with up to 5 labels and 50 value combinations
+  - Metric validation following Prometheus naming conventions
+- Metric Export/Import:
+  - JSON-based configuration export for backup
+  - Import with three modes: skip existing, overwrite, or rename duplicates
+  - Version tracking in export format
+- Grafana Dashboard Templates:
+  - WordPress Overview dashboard (users, posts, comments, cron, transients)
+  - WordPress Runtime dashboard (HTTP requests, database queries)
+  - WordPress WooCommerce dashboard (orders, revenue, products, customers)
+  - Easy download and import instructions
+- New "Custom Metrics" tab in admin settings
+- New "Dashboards" tab in admin settings
+- Reset runtime metrics button to clear accumulated data
+
+### Changed
+
+- Settings page now has 5 tabs: License, Metrics, Custom Metrics, Dashboards, Help
+- Updated translations with all new strings
+
+## [0.2.2] - 2026-02-02
+
+### Fixed
+
+- Fixed `wc_orders_count()` call missing required status parameter in WooCommerce orders metrics
+
+## [0.2.1] - 2026-02-02
+
+### Added
+
+- Localhost license bypass for development environments (localhost, 127.0.0.1, ::1, \*.localhost, \*.local)
+- Automatic rewrite rules flush when license status changes
+
+### Fixed
+
+- Fixed 404 error on `/metrics` endpoint when license becomes valid after plugin activation
+
+## [0.2.0] - 2026-02-02
+
+### Added
+
+- WooCommerce integration metrics (when WooCommerce is active):
+  - `wordpress_woocommerce_products_total` - Products by status and type
+  - `wordpress_woocommerce_orders_total` - Orders by status
+  - `wordpress_woocommerce_revenue_total` - Revenue (all time, today, month)
+  - `wordpress_woocommerce_customers_total` - Customers (registered, guest)
+- Cron job metrics:
+  - `wordpress_cron_events_total` - Scheduled cron events by hook
+  - `wordpress_cron_overdue_total` - Number of overdue cron events
+  - `wordpress_cron_next_run_timestamp` - Unix timestamp of next scheduled cron
+- Transient cache metrics:
+  - `wordpress_transients_total` - Transients by type (total, with_expiration, persistent, expired)
+- WooCommerce metrics section in settings (only visible when WooCommerce is active)
+- Support for WooCommerce HPOS (High-Performance Order Storage)
+
+### Changed
+
+- Updated Help tab with new metrics reference
+
 ## [0.1.1] - 2026-02-02
 
 ### Changed

CLAUDE.md

@@ -15,8 +15,15 @@ This plugin provides a Prometheus `/metrics` endpoint and an extensible way to a
 - Prometheus compatible authenticated `/metrics` endpoint
 - Optional default metrics (users, posts, comments, plugins)
 - Runtime metrics (HTTP requests, request duration, database queries)
+- Cron job metrics (scheduled events, overdue, next run)
+- Transient cache metrics (total, expiring, expired)
+- WooCommerce integration (products, orders, revenue, customers)
+- Custom metric builder with admin UI (gauges with static or option-based values)
+- Metric export/import for backup and site migration
+- Grafana dashboard templates for easy visualization
 - Dedicated plugin settings under 'Settings/Metrics' menu
 - Extensible by other plugins using `wp_prometheus_collect_metrics` action hook
+- Dashboard extension hook `wp_prometheus_register_dashboards` for third-party Grafana dashboards
 - License management integration
 
 ### Key Fact: 100% AI-Generated
@@ -27,11 +34,9 @@ This project is proudly **"vibe-coded"** using Claude.AI - the entire codebase w
 
 **Note for AI Assistants:** Clean this section after the specific features are done or new releases are made. Effective changes are tracked in `CHANGELOG.md`. Do not add completed versions here - document them in the Session History section at the end of this file.
 
-### Version 0.2.0 (Planned)
+### Known Bugs
 
-- WooCommerce integration metrics
-- Cron job metrics
-- Transient cache metrics
+*No known bugs at this time.*
 
 ## Technical Stack
 
@@ -76,11 +81,7 @@ Text domain: `wp-prometheus`
 - `en_US` - English (United States) [base language - .pot template]
 - `de_CH` - German (Switzerland, formal)
 
-To compile translations to .mo files for production:
-
-```bash
-for po in languages/*.po; do msgfmt -o "${po%.po}.mo" "$po"; done
-```
+Translation compilation (.po → .mo) is handled automatically by CI/CD pipeline during release builds. No local compilation needed.
 
 ### Create releases
 
@@ -208,9 +209,13 @@ When editing CLAUDE.md or other markdown files, follow these rules to avoid lint
 ```txt
 wp-prometheus/
 ├── .gitea/workflows/
-│   └── release.yml          # CI/CD pipeline
+│   └── release.yml          # CI/CD pipeline (test + build)
 ├── assets/
 │   ├── css/                  # Admin/Frontend styles
+│   ├── dashboards/           # Grafana dashboard templates
+│   │   ├── wordpress-overview.json
+│   │   ├── wordpress-runtime.json
+│   │   └── wordpress-woocommerce.json
 │   └── js/
 │       └── admin.js          # Admin JavaScript
 ├── languages/                # Translation files
@@ -219,6 +224,7 @@ wp-prometheus/
 ├── releases/                 # Release packages
 ├── src/
 │   ├── Admin/
+│   │   ├── DashboardProvider.php # Grafana dashboard provider
 │   │   └── Settings.php      # Settings page
 │   ├── Endpoint/
 │   │   └── MetricsEndpoint.php  # /metrics endpoint
@@ -226,14 +232,34 @@ wp-prometheus/
 │   │   └── Manager.php       # License management
 │   ├── Metrics/
 │   │   ├── Collector.php        # Prometheus metrics collector
-│   │   └── RuntimeCollector.php # Runtime metrics collector
+│   │   ├── CustomMetricBuilder.php # Custom metric CRUD
+│   │   ├── RuntimeCollector.php # Runtime metrics collector
+│   │   └── StorageFactory.php   # Storage adapter factory
 │   ├── Installer.php         # Activation/Deactivation
 │   ├── Plugin.php            # Main plugin class
 │   └── index.php
+├── tests/
+│   ├── bootstrap.php         # WP constants + function stubs
+│   ├── Helpers/
+│   │   └── GlobalFunctionState.php  # Controllable stub state
+│   └── Unit/
+│       ├── TestCase.php      # Base class with PHPMock
+│       ├── AuthenticationTest.php
+│       ├── InstallerTest.php
+│       ├── Admin/
+│       │   └── DashboardProviderTest.php
+│       ├── Endpoint/
+│       │   └── MetricsEndpointTest.php
+│       └── Metrics/
+│           ├── CollectorTest.php
+│           ├── CustomMetricBuilderTest.php
+│           ├── RuntimeCollectorTest.php
+│           └── StorageFactoryTest.php
 ├── CHANGELOG.md
 ├── CLAUDE.md
 ├── composer.json
 ├── index.php
+├── phpunit.xml               # PHPUnit 10 configuration
 ├── PLAN.md
 ├── README.md
 ├── uninstall.php
@@ -282,6 +308,288 @@ add_action( 'wp_prometheus_collect_metrics', function( $collector ) {
 
 ## Session History
 
+### 2026-02-26 - PHPUnit Test Suite & CI/CD Integration (v0.5.0)
+
+- Created comprehensive PHPUnit test suite with 189 tests and 329 assertions
+- Added `php-mock/php-mock-phpunit:^2.10` to composer.json require-dev
+- Created test infrastructure:
+  - `tests/bootstrap.php`: ~45 WordPress function stubs with `if (!function_exists())` guards
+  - `tests/Helpers/GlobalFunctionState.php`: Static class for controlling stub behavior
+  - `tests/Unit/TestCase.php`: Abstract base class with PHPMock trait
+- 8 test classes covering all core plugin classes:
+  - `CustomMetricBuilderTest` (35 tests) - validation, CRUD, import/export
+  - `StorageFactoryTest` (25 tests) - adapter config, env vars, connection tests
+  - `AuthenticationTest` (13 tests) - Bearer/query auth, header extraction
+  - `DashboardProviderTest` (27 tests) - registration, path traversal security
+  - `RuntimeCollectorTest` (22 tests) - endpoint normalization, histograms
+  - `InstallerTest` (11 tests) - activate, deactivate, uninstall cleanup
+  - `CollectorTest` (10 tests) - registry, register_gauge/counter/histogram, render
+  - `MetricsEndpointTest` (5 tests) - rewrite rules, request routing
+- Added `test` job to `.gitea/workflows/release.yml` that gates `build-release`
+- **Key Learning**: php-mock/php-mock-phpunit for WordPress testing without WP environment
+  - Intercepts unqualified function calls in namespaced code via PHP namespace fallback
+  - `$this->getFunctionMock('Namespace', 'function_name')` creates expectations
+  - Does NOT work for functions called from global namespace (bootstrap stubs) or in PHP 8.4 for some edge cases
+  - Solution for global-scope stubs: Make them controllable via `GlobalFunctionState::$options`
+- **Key Learning**: Testing singletons and static state
+  - Use `ReflectionClass::newInstanceWithoutConstructor()` to bypass private constructors
+  - Reset static `$instance` properties via `ReflectionProperty::setValue(null, null)` in tearDown
+  - Always reset StorageFactory and RuntimeCollector singletons between tests
+- **Key Learning**: CI/CD pipeline structure for test gating
+  - `test` job uses `composer install` (WITH dev deps) to run tests
+  - `build-release` job uses `--no-dev` (unchanged) for production builds
+  - `needs: test` dependency ensures failing tests block releases
+
+### 2026-02-26 - Security Audit & Refactoring (v0.4.9)
+
+- Fixed XSS vulnerabilities in admin.js (jQuery `.html()` → safe DOM construction)
+- Fixed insecure token generation (`Math.random()` → Web Crypto API)
+- Added 1 MB import size limit, import mode validation, removed `site_url` from exports
+- Extracted shared authentication logic and helper methods
+- Optimized WooCommerce product counting with COUNT query
+
+### 2026-02-07 - Fix Early Textdomain Loading (v0.4.8)
+
+- Fixed `_load_textdomain_just_in_time` warning on admin pages (WordPress 6.7+ compatibility)
+- Root cause: `load_plugin_textdomain()` was called during `plugins_loaded` in `Plugin::__construct()`
+- WordPress 6.7+ requires textdomain loading at the `init` action or later
+- Three classes needed fixing:
+  - `Plugin.php`: Deferred `load_textdomain()` to `init` action hook, changed method visibility to public
+  - `Settings.php`: Deferred tab label initialization (which uses `__()`) to a lazy `get_tabs()` method
+  - `DashboardProvider.php`: Deferred built-in dashboard definitions (with `__()` calls) to a lazy `get_builtin_dashboards()` method
+- Cleared Known Bugs section — no remaining known issues
+- **Key Learning**: WordPress 6.7 textdomain loading requirements
+  - `load_plugin_textdomain()` must be called at `init` or later
+  - WordPress's JIT textdomain loader (`_load_textdomain_just_in_time`) also triggers too-early warnings
+  - Any `__()` / `_e()` calls before `init` for a plugin textdomain will trigger the notice
+  - The warning causes "headers already sent" errors because the notice output breaks header modifications
+  - Solution: Defer both explicit `load_plugin_textdomain()` and any `__()` calls to `init` or later hooks
+
+### 2026-02-03 - Database Query Timing Documentation (v0.4.7)
+
+- Added database query duration distribution panel to Grafana Runtime dashboard
+- Added `wordpress_db_query_duration_seconds` metric to Help tab metrics reference
+- Added documentation in README explaining how to enable `SAVEQUERIES` for query timing
+- Updated translation files (.pot and .po) with new strings
+- **Key Learning**: WordPress `SAVEQUERIES` constant
+  - Enables `$wpdb->queries` array with query strings, timing, and call stacks
+  - Required for `wordpress_db_query_duration_seconds` histogram metric
+  - Has performance overhead - recommended for development, use cautiously in production
+  - Without it, only query counts are available (not timing data)
+
+### 2026-02-03 - Dashboard Extension Hook (v0.4.6)
+
+- Added `wp_prometheus_register_dashboards` action hook for third-party plugins
+- Third-party plugins can now register their own Grafana dashboard templates
+- Implementation in `DashboardProvider.php`:
+  - `register_dashboard(slug, args)` method for registrations
+  - Supports file-based dashboards (absolute path to JSON) or inline JSON content
+  - Security: Path traversal protection (files must be under `WP_CONTENT_DIR`)
+  - `fire_registration_hook()` with output buffering and exception handling
+  - Respects isolated mode setting (skips third-party hooks when enabled)
+  - `is_third_party()` and `get_plugin_name()` helper methods
+- Updated admin UI in Settings.php:
+  - "Extension" badge displayed on third-party dashboard cards
+  - Plugin attribution shown below third-party dashboards
+  - Visual distinction with blue border for third-party cards
+- **Key Learning**: Extension hook design pattern
+  - Fire hook lazily on first `get_available()` call, not in constructor
+  - Use `$hook_fired` flag to prevent double-firing
+  - Wrap hook execution in try-catch to isolate failures
+  - Validate registrations thoroughly before accepting them
+- **Key Learning**: Security for file-based registrations
+  - Require absolute paths (`path_is_absolute()`)
+  - Validate files exist and are readable
+  - Use `realpath()` to resolve symlinks and prevent traversal
+  - Restrict to `WP_CONTENT_DIR` (not just plugin directories)
+
+### 2026-02-02 - Settings Persistence Fix (v0.4.5)
+
+- Fixed critical bug where settings would get cleared when saving from different Metrics sub-tabs
+- Root cause: All settings were registered under single `wp_prometheus_metrics_settings` group
+  - When saving from "Endpoint" sub-tab, only auth token was in POST data
+  - WordPress Settings API would process all registered settings in the group
+  - Missing fields (enabled_metrics, isolated_mode) would receive null/undefined
+  - Sanitize callbacks returned empty values, overwriting existing settings
+- Solution: Split into separate settings groups per sub-tab:
+  - `wp_prometheus_endpoint_settings` for auth token
+  - `wp_prometheus_selection_settings` for enabled metrics
+  - `wp_prometheus_advanced_settings` for isolated mode
+- **Key Learning**: WordPress Settings API and multiple forms
+  - When multiple forms share the same settings group, saving one form can clear settings from another
+  - Each form with `settings_fields()` should use a unique option group
+  - `register_setting()` group name must match `settings_fields()` group name
+
+### 2026-02-02 - Safe Mode & Custom Hooks Fix (v0.4.4)
+
+- Redesigned metrics collection to support both plugin compatibility AND custom metrics:
+  - **Safe Mode (default)**: Removes content filters early but lets WordPress load normally
+  - **Isolated Mode**: Legacy early mode that skips custom hooks entirely
+- Implementation:
+  - `WP_PROMETHEUS_METRICS_REQUEST` constant set for any /metrics request
+  - Content filters removed via `plugins_loaded` hook at priority 0
+  - Collector fires `wp_prometheus_collect_metrics` with protection (output buffering, try-catch)
+  - `wp_prometheus_isolated_mode` option replaces `wp_prometheus_disable_early_mode`
+  - `WP_PROMETHEUS_ISOLATED_MODE` environment variable for containerized deployments
+- Collector now wraps custom hooks in `fire_custom_metrics_hook()` method:
+  - Removes content filters again before hook (in case re-added)
+  - Uses output buffering to discard accidental output
+  - Catches exceptions to prevent breaking metrics output
+  - Logs errors when WP_DEBUG is enabled
+- Updated admin UI with mode comparison table
+- **Key Learning**: Hybrid approach for plugin compatibility
+  - The memory issue comes from content filter recursion, not just plugin loading
+  - Removing filters early (before any plugin can trigger them) prevents recursion
+  - Plugins still load and can register their `wp_prometheus_collect_metrics` hooks
+  - Hooks fire after filters are removed, in a protected context
+- **Key Learning**: Defense in depth for custom hooks
+  - Remove filters again right before hook fires (plugins may re-add them)
+  - Output buffering catches any echo/print from misbehaving plugins
+  - Try-catch prevents one broken plugin from breaking metrics entirely
+
+### 2026-02-02 - Sub-tabs & Early Mode Fix (v0.4.3)
+
+- Split Metrics tab into sub-tabs for better organization:
+  - **Endpoint**: Authentication token configuration
+  - **Selection**: Enable/disable individual metrics
+  - **Runtime**: Reset runtime metrics data
+  - **Advanced**: Early mode toggle and status
+- Fixed early mode setting not being saved (was outside form element)
+- Added CSS styling for horizontal sub-tab navigation
+- **Key Learning**: WordPress Settings API form structure
+  - Settings must be inside `<form action="options.php">` with `settings_fields()` call
+  - Each sub-tab needs its own form wrapper for proper saving
+  - Sub-tabs use URL query parameter (`subtab`) within the main tab
+- **Key Learning**: WordPress plugin versioning requires TWO updates
+  - Plugin header comment `Version: x.x.x` (line ~6) - used by WordPress admin
+  - PHP constant `WP_PROMETHEUS_VERSION` (line ~133) - used internally
+  - CI/CD checks both must match the git tag, causing release failures if mismatched
+
+### 2026-02-02 - Early Mode Toggle (v0.4.2)
+
+- Added option to disable early mode for users who need extensibility
+- Implementation:
+  - Added `wp_prometheus_disable_early_mode` WordPress option
+  - Added `WP_PROMETHEUS_DISABLE_EARLY_MODE` environment variable support
+  - Option check in `wp_prometheus_early_metrics_check()` before early interception
+  - Environment variable accepts `1`, `true`, `yes`, `on` (case-insensitive)
+- Admin UI in Metrics tab:
+  - "Early Mode" section with description of functionality
+  - Checkbox to disable early metrics interception
+  - Environment override notice when env var is set
+  - Current status indicator showing early mode state
+- **Key Learning**: Balancing compatibility vs extensibility
+  - Early mode fixes memory issues but disables `wp_prometheus_collect_metrics` hook
+  - Users with custom metrics need the hook, so early mode must be optional
+  - Default remains enabled (safe) with explicit opt-out for advanced users
+
+### 2026-02-02 - Plugin Compatibility Fix (v0.4.1)
+
+- Fixed memory exhaustion (1GB limit) when wp-fedistream (Twig-based) plugin is active
+- Root cause: Infinite recursion through WordPress hook system when content filters trigger Twig rendering
+- Solution: Early metrics endpoint interception before full WordPress initialization
+- Implementation changes:
+  - Added `wp_prometheus_early_metrics_check()` in bootstrap file (wp-prometheus.php)
+  - Checks REQUEST_URI for `/metrics` pattern before `plugins_loaded` fires
+  - Defines `WP_PROMETHEUS_EARLY_METRICS` constant to signal early mode
+  - Removes content filters (`the_content`, `the_excerpt`, `get_the_excerpt`, `the_title`)
+  - Collector skips `wp_prometheus_collect_metrics` action in early mode
+  - Changed MetricsEndpoint from `template_redirect` to `parse_request` hook
+- **Key Learning**: WordPress plugin loading order and hook timing
+  - Plugins load alphabetically, so wp-fedistream ('f') loads before wp-prometheus ('p')
+  - `template_redirect` fires too late - after themes and Twig initialize
+  - `parse_request` fires earlier but still after plugin files load
+  - Earliest interception point: top-level code in plugin bootstrap file
+- **Key Learning**: Content filter recursion in WordPress
+  - `get_the_excerpt()` internally triggers `apply_filters('the_content', ...)`
+  - This creates unexpected recursion vectors when Twig templates process content
+  - Solution: Remove all content-related filters before metrics collection
+- **Key Learning**: Isolating metrics collection from WordPress template system
+  - Use `remove_all_filters()` to clear problematic filter chains
+  - Skip extensibility hooks (`do_action`) when in isolated early mode
+  - Exit immediately after output to prevent further WordPress processing
+
+### 2026-02-02 - Persistent Storage (v0.4.0)
+
+- Added persistent storage support for metrics:
+  - `StorageFactory.php` - Factory class for storage adapter instantiation
+  - Redis storage adapter for shared metrics across multiple instances
+  - APCu storage adapter for single-server high-performance caching
+  - Automatic fallback to In-Memory if configured adapter fails
+- Added new "Storage" tab in admin settings:
+  - Storage adapter selection (In-Memory, Redis, APCu)
+  - Redis configuration (host, port, password, database, key prefix)
+  - APCu configuration (key prefix)
+  - Connection test button with detailed error messages
+- Added environment variable support for Docker deployments:
+  - `WP_PROMETHEUS_STORAGE_ADAPTER` - Adapter selection
+  - `WP_PROMETHEUS_REDIS_HOST`, `_PORT`, `_PASSWORD`, `_DATABASE`, `_PREFIX`
+  - `WP_PROMETHEUS_APCU_PREFIX`
+  - Environment variables take precedence over admin settings
+- Updated `Collector.php` to use `StorageFactory::get_adapter()`
+- Updated Help tab with storage backends documentation
+- Updated translation files with all new strings
+- **Key Learning**: promphp/prometheus_client_php storage adapters
+  - Redis adapter requires options array with host, port, password, timeout
+  - APCu adapter just needs a prefix string
+  - Use `Redis::setPrefix()` before instantiation for custom key prefixes
+- **Key Learning**: Docker environment variable configuration
+  - Use `getenv()` with explicit false check (`false !== getenv()`)
+  - Environment variables should override WordPress options for containerized deployments
+
+### 2026-02-02 - Custom Metrics & Dashboards (v0.3.0)
+
+- Added Custom Metric Builder with full admin UI:
+  - `CustomMetricBuilder.php` - CRUD operations, validation, export/import
+  - Support for static values and WordPress option-based values
+  - Label support (max 5 labels, 50 value combinations)
+  - Prometheus naming convention validation (`[a-zA-Z_:][a-zA-Z0-9_:]*`)
+- Added Grafana Dashboard Templates:
+  - `DashboardProvider.php` - Dashboard file provider with path traversal protection
+  - `wordpress-overview.json` - General WordPress metrics
+  - `wordpress-runtime.json` - HTTP/DB performance metrics
+  - `wordpress-woocommerce.json` - WooCommerce store metrics
+- Added export/import functionality:
+  - JSON-based configuration export
+  - Three import modes: skip, overwrite, rename duplicates
+  - Version tracking in export format
+- Updated Settings page with new tabs:
+  - "Custom Metrics" tab with metric form and table
+  - "Dashboards" tab with download buttons
+  - "Reset Runtime Metrics" button in Metrics tab
+- Updated `Collector.php` to integrate custom metrics
+- Updated translation files with all new strings
+- **Key Learning**: Dynamic form handling in WordPress admin
+  - Use `wp_create_nonce()` with unique nonce names per AJAX action
+  - Localize script with `wp_localize_script()` for nonces and AJAX URL
+  - Always verify `current_user_can('manage_options')` in AJAX handlers
+- **Key Learning**: Grafana dashboard JSON format
+  - Use `${DS_PROMETHEUS}` for data source variable
+  - Schema version 39 for current Grafana compatibility
+  - Panels use `gridPos` for layout positioning
+
+### 2026-02-02 - Extended Metrics (v0.2.0)
+
+- Added WooCommerce integration metrics (only when WooCommerce is active):
+  - `wordpress_woocommerce_products_total` - Products by status and type
+  - `wordpress_woocommerce_orders_total` - Orders by status
+  - `wordpress_woocommerce_revenue_total` - Revenue (all time, today, month)
+  - `wordpress_woocommerce_customers_total` - Customers (registered, guest)
+- Added cron job metrics:
+  - `wordpress_cron_events_total` - Scheduled cron events by hook (top 20)
+  - `wordpress_cron_overdue_total` - Number of overdue cron events
+  - `wordpress_cron_next_run_timestamp` - Unix timestamp of next scheduled cron
+- Added transient cache metrics:
+  - `wordpress_transients_total` - Transients by type (total, with_expiration, persistent, expired)
+- Updated Settings page with new metric categories
+- Updated Help tab with new metrics reference
+- **Key Learning**: WooCommerce HPOS (High-Performance Order Storage) requires different queries
+  - Check `OrderUtil::custom_orders_table_usage_is_enabled()` to determine storage type
+  - HPOS uses `wc_orders` table instead of `posts` and `postmeta`
+- **Key Learning**: Cron event labeling requires cardinality control
+  - Limit to top 20 hooks to prevent label explosion
+  - Use `arsort()` to get most frequent hooks first
+
 ### 2026-02-02 - Runtime Metrics (v0.1.0)
 
 - Implemented runtime metrics collection for HTTP requests and database queries

PLAN.md

@@ -59,6 +59,7 @@ wp-prometheus/
 │   └── release.yml          # CI/CD pipeline
 ├── assets/
 │   ├── css/                  # Admin/Frontend styles
+│   ├── dashboards/           # Grafana dashboard templates
 │   └── js/
 │       └── admin.js          # Admin JavaScript
 ├── languages/                # Translation files
@@ -67,13 +68,17 @@ wp-prometheus/
 ├── releases/                 # Release packages
 ├── src/
 │   ├── Admin/
+│   │   ├── DashboardProvider.php
 │   │   └── Settings.php
 │   ├── Endpoint/
 │   │   └── MetricsEndpoint.php
 │   ├── License/
 │   │   └── Manager.php
 │   ├── Metrics/
-│   │   └── Collector.php
+│   │   ├── Collector.php
+│   │   ├── CustomMetricBuilder.php
+│   │   ├── RuntimeCollector.php
+│   │   └── StorageFactory.php
 │   ├── Installer.php
 │   ├── Plugin.php
 │   └── index.php
@@ -159,19 +164,57 @@ Alternatively, the token can be passed as a query parameter (for testing):
 https://example.com/metrics/?token=your-auth-token
 ```
 
+## Storage Configuration
+
+The plugin supports multiple storage backends for Prometheus metrics:
+
+### Available Adapters
+
+| Adapter   | Description                     | Use Case                              |
+| --------- | ------------------------------- | ------------------------------------- |
+| In-Memory | Default, no persistence         | Development, single request metrics   |
+| Redis     | Shared storage across instances | Production, load-balanced environments|
+| APCu      | High-performance local cache    | Production, single-server deployments |
+
+### Environment Variables
+
+For Docker or containerized environments, configure storage via environment variables:
+
+```bash
+# Storage adapter selection
+WP_PROMETHEUS_STORAGE_ADAPTER=redis
+
+# Redis configuration
+WP_PROMETHEUS_REDIS_HOST=redis
+WP_PROMETHEUS_REDIS_PORT=6379
+WP_PROMETHEUS_REDIS_PASSWORD=secret
+WP_PROMETHEUS_REDIS_DATABASE=0
+WP_PROMETHEUS_REDIS_PREFIX=WORDPRESS_PROMETHEUS_
+
+# APCu configuration
+WP_PROMETHEUS_APCU_PREFIX=wp_prom
+```
+
+### Docker Compose Example
+
+```yaml
+services:
+  wordpress:
+    image: wordpress:latest
+    environment:
+      WP_PROMETHEUS_STORAGE_ADAPTER: redis
+      WP_PROMETHEUS_REDIS_HOST: redis
+      WP_PROMETHEUS_REDIS_PORT: 6379
+    depends_on:
+      - redis
+
+  redis:
+    image: redis:alpine
+```
+
 ## Future Enhancements
 
-### Version 0.2.0
-
-- WooCommerce integration metrics
-- Cron job metrics
-- Transient cache metrics
-
-### Version 0.3.0
-
-- Custom metric builder in admin
-- Metric export/import
-- Grafana dashboard templates
+*No planned features at this time.*
 
 ## Dependencies
 

README.md

@@ -6,7 +6,13 @@ A WordPress plugin that provides a Prometheus-compatible `/metrics` endpoint wit
 
 - Prometheus-compatible authenticated `/metrics` endpoint
 - Default WordPress metrics (users, posts, comments, plugins)
+- Runtime metrics (HTTP requests, database queries)
+- Cron job and transient cache metrics
+- WooCommerce integration (products, orders, revenue)
+- Custom metric builder with admin UI
+- Grafana dashboard templates with download
 - Extensible by other plugins using hooks
+- Dashboard extension hook for third-party Grafana dashboards
 - Settings page under Settings > Metrics
 - Bearer token authentication
 - License management integration
@@ -92,6 +98,48 @@ scrape_configs:
 
 **Note:** Runtime metrics aggregate data across requests. Enable only the metrics you need to minimize performance impact.
 
+#### Enabling Database Query Timing
+
+The `wordpress_db_query_duration_seconds` histogram requires WordPress's `SAVEQUERIES` constant to be enabled. Add this to your `wp-config.php`:
+
+```php
+define( 'SAVEQUERIES', true );
+```
+
+**Important considerations:**
+
+- `SAVEQUERIES` has a performance overhead as it logs all queries with timing and call stacks
+- Recommended for development/staging environments, use with caution in production
+- Without `SAVEQUERIES`, only query counts (`wordpress_db_queries_total`) are available
+- The histogram shows total query time per request, grouped by endpoint
+
+### Cron Metrics (v0.2.0+)
+
+| Metric | Type | Labels | Description |
+|--------|------|--------|-------------|
+| wordpress_cron_events_total | Gauge | hook | Scheduled cron events by hook |
+| wordpress_cron_overdue_total | Gauge | - | Number of overdue cron events |
+| wordpress_cron_next_run_timestamp | Gauge | - | Unix timestamp of next scheduled cron |
+
+### Transient Metrics (v0.2.0+)
+
+| Metric | Type | Labels | Description |
+|--------|------|--------|-------------|
+| wordpress_transients_total | Gauge | type | Transients by type (total, with_expiration, persistent, expired) |
+
+### WooCommerce Metrics (v0.2.0+)
+
+These metrics are only available when WooCommerce is active.
+
+| Metric | Type | Labels | Description |
+|--------|------|--------|-------------|
+| wordpress_woocommerce_products_total | Gauge | status, type | Products by status and type |
+| wordpress_woocommerce_orders_total | Gauge | status | Orders by status |
+| wordpress_woocommerce_revenue_total | Gauge | period, currency | Revenue (all_time, today, month) |
+| wordpress_woocommerce_customers_total | Gauge | type | Customers (registered, guest) |
+
+**Note:** WooCommerce metrics support both legacy post-based orders and HPOS (High-Performance Order Storage).
+
 ## Extending with Custom Metrics
 
 Add your own metrics using the `wp_prometheus_collect_metrics` action:
@@ -127,8 +175,93 @@ $histogram = $collector->register_histogram( $name, $help, $labels, $buckets );
 $histogram->observe( $value, $labelValues );
 ```
 
+## Extending with Custom Dashboards (v0.4.6+)
+
+Add your own Grafana dashboard templates using the `wp_prometheus_register_dashboards` action:
+
+```php
+add_action( 'wp_prometheus_register_dashboards', function( $provider ) {
+    // File-based dashboard
+    $provider->register_dashboard( 'my-plugin-dashboard', array(
+        'title'       => __( 'My Plugin Metrics', 'my-plugin' ),
+        'description' => __( 'Dashboard for my custom metrics', 'my-plugin' ),
+        'icon'        => 'dashicons-chart-bar',
+        'file'        => MY_PLUGIN_PATH . 'assets/dashboards/my-dashboard.json',
+        'plugin'      => 'My Plugin Name',
+    ) );
+
+    // OR inline JSON dashboard
+    $provider->register_dashboard( 'dynamic-dashboard', array(
+        'title'       => __( 'Dynamic Dashboard', 'my-plugin' ),
+        'description' => __( 'Dynamically generated dashboard', 'my-plugin' ),
+        'icon'        => 'dashicons-admin-generic',
+        'json'        => json_encode( $dashboard_array ),
+        'plugin'      => 'My Plugin Name',
+    ) );
+} );
+```
+
+### Registration Parameters
+
+| Parameter | Required | Description |
+| --------- | -------- | ----------- |
+| `title` | Yes | Dashboard title displayed in admin |
+| `description` | No | Description shown below the title |
+| `icon` | No | Dashicon class (default: `dashicons-chart-line`) |
+| `file` | Yes* | Absolute path to JSON file |
+| `json` | Yes* | Inline JSON content |
+| `plugin` | No | Plugin name for attribution |
+
+*Either `file` or `json` is required, but not both.
+
+### Security Notes
+
+- File paths must be absolute and within `wp-content/`
+- Inline JSON is validated during registration
+- Third-party dashboards are marked with an "Extension" badge in the admin UI
+
 ## Development
 
+### Testing
+
+The plugin includes a comprehensive PHPUnit test suite with 189 tests covering all core classes.
+
+```bash
+# Install dependencies (including dev)
+composer install
+
+# Run the full test suite
+composer test
+```
+
+#### Test Architecture
+
+Tests use [php-mock/php-mock-phpunit](https://github.com/php-mock/php-mock-phpunit) to mock WordPress functions called from namespaced plugin code, and a `GlobalFunctionState` helper for controlling global-scope function stubs (authentication, options, conditionals).
+
+```
+tests/
+├── bootstrap.php                         # WP constants + function stubs
+├── Helpers/
+│   └── GlobalFunctionState.php           # Controllable state for stubs
+└── Unit/
+    ├── TestCase.php                      # Base class with PHPMock trait
+    ├── AuthenticationTest.php            # Bearer/query auth, header extraction
+    ├── InstallerTest.php                 # Activate, deactivate, uninstall
+    ├── Metrics/
+    │   ├── CustomMetricBuilderTest.php   # Validation, CRUD, import/export
+    │   ├── RuntimeCollectorTest.php      # Endpoint normalization, histograms
+    │   ├── StorageFactoryTest.php        # Adapter config, env vars, connections
+    │   └── CollectorTest.php             # Registry, register_*, render
+    ├── Admin/
+    │   └── DashboardProviderTest.php     # Registration, path security
+    └── Endpoint/
+        └── MetricsEndpointTest.php       # Rewrite rules, request routing
+```
+
+#### CI/CD Integration
+
+Tests run automatically in the Gitea CI/CD pipeline before release builds. A failing test suite blocks the release.
+
 ### Build for Release
 
 ```bash

assets/css/admin.css

@@ -9,6 +9,61 @@
     margin-top: 20px;
 }
 
+/* Sub-tabs navigation */
+.wp-prometheus-subtabs {
+    margin-top: 15px;
+}
+
+.wp-prometheus-subtab-nav {
+    display: flex;
+    margin: 0;
+    padding: 0;
+    list-style: none;
+    border-bottom: 1px solid #c3c4c7;
+}
+
+.wp-prometheus-subtab-item {
+    margin: 0;
+    padding: 0;
+}
+
+.wp-prometheus-subtab-item a {
+    display: block;
+    padding: 8px 16px;
+    text-decoration: none;
+    color: #50575e;
+    border: 1px solid transparent;
+    border-bottom: none;
+    margin-bottom: -1px;
+    background: transparent;
+    font-size: 13px;
+    font-weight: 400;
+}
+
+.wp-prometheus-subtab-item a:hover {
+    color: #2271b1;
+    background: #f6f7f7;
+}
+
+.wp-prometheus-subtab-item.active a {
+    color: #1d2327;
+    background: #fff;
+    border-color: #c3c4c7;
+    border-bottom-color: #fff;
+    font-weight: 600;
+}
+
+.wp-prometheus-subtab-content {
+    background: #fff;
+    border: 1px solid #c3c4c7;
+    border-top: none;
+    padding: 20px;
+}
+
+.wp-prometheus-subtab-content h3:first-child {
+    margin-top: 0;
+}
+
 /* License status box */
 .wp-prometheus-license-status {
     margin: 15px 0;
@@ -45,3 +100,189 @@
 .wp-prometheus-tab-content .form-table {
     margin-top: 10px;
 }
+
+/* Custom metrics form */
+.wp-prometheus-metric-form {
+    background: #fff;
+    border: 1px solid #ccd0d4;
+    border-radius: 4px;
+    padding: 20px;
+    margin: 20px 0;
+}
+
+.wp-prometheus-metric-form h3 {
+    margin-top: 0;
+    padding-bottom: 10px;
+    border-bottom: 1px solid #eee;
+}
+
+.wp-prometheus-metric-form .required {
+    color: #d63638;
+}
+
+/* Label rows */
+.metric-label-row {
+    display: flex;
+    align-items: center;
+    gap: 10px;
+    margin-bottom: 8px;
+}
+
+.metric-label-row input {
+    flex: 1;
+    max-width: 300px;
+}
+
+.metric-label-row .remove-label {
+    padding: 0 8px;
+    min-width: auto;
+}
+
+/* Value rows */
+.metric-value-row {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+    margin-bottom: 8px;
+    flex-wrap: wrap;
+}
+
+.metric-value-row input {
+    width: 120px;
+}
+
+.metric-value-row .remove-value-row {
+    padding: 0 8px;
+    min-width: auto;
+}
+
+/* Custom metrics table */
+.wp-prometheus-custom-metrics .wp-list-table code {
+    background: #f0f0f1;
+    padding: 2px 6px;
+    border-radius: 3px;
+}
+
+.wp-prometheus-custom-metrics .wp-list-table td {
+    vertical-align: middle;
+}
+
+.wp-prometheus-custom-metrics .wp-list-table .dashicons {
+    font-size: 18px;
+    width: 18px;
+    height: 18px;
+}
+
+/* Dashboard grid */
+.wp-prometheus-dashboard-grid {
+    display: grid;
+    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
+    gap: 20px;
+    margin: 20px 0;
+}
+
+.wp-prometheus-dashboard-card {
+    background: #fff;
+    border: 1px solid #ccd0d4;
+    border-radius: 4px;
+    padding: 20px;
+    text-align: center;
+    transition: box-shadow 0.2s ease;
+}
+
+.wp-prometheus-dashboard-card:hover {
+    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
+}
+
+.wp-prometheus-dashboard-card .dashboard-icon {
+    margin-bottom: 15px;
+}
+
+.wp-prometheus-dashboard-card .dashboard-icon .dashicons {
+    font-size: 48px;
+    width: 48px;
+    height: 48px;
+    color: #2271b1;
+}
+
+.wp-prometheus-dashboard-card h3 {
+    margin: 0 0 10px 0;
+    font-size: 16px;
+}
+
+.wp-prometheus-dashboard-card p {
+    color: #646970;
+    margin: 0 0 15px 0;
+    font-size: 13px;
+}
+
+/* Third-party dashboard card styling */
+.wp-prometheus-dashboard-card.third-party {
+    position: relative;
+    border-color: #2271b1;
+}
+
+.wp-prometheus-dashboard-card .dashboard-badge {
+    position: absolute;
+    top: -8px;
+    right: -8px;
+    background: #2271b1;
+    color: #fff;
+    font-size: 10px;
+    font-weight: 600;
+    padding: 3px 8px;
+    border-radius: 10px;
+    text-transform: uppercase;
+    letter-spacing: 0.5px;
+}
+
+.wp-prometheus-dashboard-card .dashboard-plugin {
+    color: #646970;
+    margin: -5px 0 15px 0;
+    font-style: italic;
+}
+
+/* Import options panel */
+#import-options {
+    border-radius: 4px;
+}
+
+#import-options label {
+    display: block;
+    margin-bottom: 8px;
+}
+
+/* Spinner alignment */
+.spinner {
+    float: none;
+    vertical-align: middle;
+}
+
+/* Button groups */
+.wp-prometheus-tab-content .button + .button {
+    margin-left: 5px;
+}
+
+/* Notice messages in forms */
+.wp-prometheus-metric-form .notice,
+.wp-prometheus-custom-metrics .notice {
+    margin: 10px 0;
+    padding: 10px 15px;
+}
+
+/* Responsive adjustments */
+@media screen and (max-width: 782px) {
+    .wp-prometheus-dashboard-grid {
+        grid-template-columns: 1fr;
+    }
+
+    .metric-value-row {
+        flex-direction: column;
+        align-items: flex-start;
+    }
+
+    .metric-value-row input {
+        width: 100%;
+        max-width: none;
+    }
+}

assets/dashboards/wordpress-overview.json

@@ -0,0 +1,851 @@
+{
+  "annotations": {
+    "list": []
+  },
+  "editable": true,
+  "fiscalYearStartMonth": 0,
+  "graphTooltip": 0,
+  "id": null,
+  "links": [],
+  "panels": [
+    {
+      "collapsed": false,
+      "gridPos": {
+        "h": 1,
+        "w": 24,
+        "x": 0,
+        "y": 0
+      },
+      "id": 1,
+      "panels": [],
+      "title": "System Info",
+      "type": "row"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "${DS_PROMETHEUS}"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "thresholds"
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": null
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 4,
+        "w": 6,
+        "x": 0,
+        "y": 1
+      },
+      "id": 2,
+      "options": {
+        "colorMode": "value",
+        "graphMode": "none",
+        "justifyMode": "auto",
+        "orientation": "auto",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "/^version$/",
+          "values": false
+        },
+        "textMode": "value"
+      },
+      "pluginVersion": "10.0.0",
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "${DS_PROMETHEUS}"
+          },
+          "editorMode": "code",
+          "expr": "wordpress_info",
+          "format": "table",
+          "instant": true,
+          "legendFormat": "__auto",
+          "refId": "A"
+        }
+      ],
+      "title": "WordPress Version",
+      "type": "stat"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "${DS_PROMETHEUS}"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "thresholds"
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": null
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 4,
+        "w": 6,
+        "x": 6,
+        "y": 1
+      },
+      "id": 3,
+      "options": {
+        "colorMode": "value",
+        "graphMode": "none",
+        "justifyMode": "auto",
+        "orientation": "auto",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "/^php_version$/",
+          "values": false
+        },
+        "textMode": "value"
+      },
+      "pluginVersion": "10.0.0",
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "${DS_PROMETHEUS}"
+          },
+          "editorMode": "code",
+          "expr": "wordpress_info",
+          "format": "table",
+          "instant": true,
+          "legendFormat": "__auto",
+          "refId": "A"
+        }
+      ],
+      "title": "PHP Version",
+      "type": "stat"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "${DS_PROMETHEUS}"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "thresholds"
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "blue",
+                "value": null
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 4,
+        "w": 6,
+        "x": 12,
+        "y": 1
+      },
+      "id": 4,
+      "options": {
+        "colorMode": "value",
+        "graphMode": "none",
+        "justifyMode": "auto",
+        "orientation": "auto",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "",
+          "values": false
+        },
+        "textMode": "auto"
+      },
+      "pluginVersion": "10.0.0",
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "${DS_PROMETHEUS}"
+          },
+          "editorMode": "code",
+          "expr": "sum(wordpress_users_total)",
+          "instant": true,
+          "legendFormat": "__auto",
+          "refId": "A"
+        }
+      ],
+      "title": "Total Users",
+      "type": "stat"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "${DS_PROMETHEUS}"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "thresholds"
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "blue",
+                "value": null
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 4,
+        "w": 6,
+        "x": 18,
+        "y": 1
+      },
+      "id": 5,
+      "options": {
+        "colorMode": "value",
+        "graphMode": "none",
+        "justifyMode": "auto",
+        "orientation": "auto",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "",
+          "values": false
+        },
+        "textMode": "auto"
+      },
+      "pluginVersion": "10.0.0",
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "${DS_PROMETHEUS}"
+          },
+          "editorMode": "code",
+          "expr": "wordpress_plugins_total{status=\"active\"}",
+          "instant": true,
+          "legendFormat": "__auto",
+          "refId": "A"
+        }
+      ],
+      "title": "Active Plugins",
+      "type": "stat"
+    },
+    {
+      "collapsed": false,
+      "gridPos": {
+        "h": 1,
+        "w": 24,
+        "x": 0,
+        "y": 5
+      },
+      "id": 6,
+      "panels": [],
+      "title": "Content",
+      "type": "row"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "${DS_PROMETHEUS}"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            }
+          },
+          "mappings": []
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 8,
+        "w": 8,
+        "x": 0,
+        "y": 6
+      },
+      "id": 7,
+      "options": {
+        "legend": {
+          "displayMode": "list",
+          "placement": "right",
+          "showLegend": true
+        },
+        "pieType": "pie",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "",
+          "values": false
+        },
+        "tooltip": {
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "${DS_PROMETHEUS}"
+          },
+          "editorMode": "code",
+          "expr": "wordpress_users_total",
+          "instant": true,
+          "legendFormat": "{{role}}",
+          "refId": "A"
+        }
+      ],
+      "title": "Users by Role",
+      "type": "piechart"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "${DS_PROMETHEUS}"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            }
+          },
+          "mappings": []
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 8,
+        "w": 8,
+        "x": 8,
+        "y": 6
+      },
+      "id": 8,
+      "options": {
+        "legend": {
+          "displayMode": "list",
+          "placement": "right",
+          "showLegend": true
+        },
+        "pieType": "pie",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "",
+          "values": false
+        },
+        "tooltip": {
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "${DS_PROMETHEUS}"
+          },
+          "editorMode": "code",
+          "expr": "wordpress_posts_total{post_type=\"post\"}",
+          "instant": true,
+          "legendFormat": "{{status}}",
+          "refId": "A"
+        }
+      ],
+      "title": "Posts by Status",
+      "type": "piechart"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "${DS_PROMETHEUS}"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            }
+          },
+          "mappings": []
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 8,
+        "w": 8,
+        "x": 16,
+        "y": 6
+      },
+      "id": 9,
+      "options": {
+        "legend": {
+          "displayMode": "list",
+          "placement": "right",
+          "showLegend": true
+        },
+        "pieType": "pie",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "",
+          "values": false
+        },
+        "tooltip": {
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "${DS_PROMETHEUS}"
+          },
+          "editorMode": "code",
+          "expr": "wordpress_comments_total{status!=\"total_comments\"}",
+          "instant": true,
+          "legendFormat": "{{status}}",
+          "refId": "A"
+        }
+      ],
+      "title": "Comments by Status",
+      "type": "piechart"
+    },
+    {
+      "collapsed": false,
+      "gridPos": {
+        "h": 1,
+        "w": 24,
+        "x": 0,
+        "y": 14
+      },
+      "id": 10,
+      "panels": [],
+      "title": "System Health",
+      "type": "row"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "${DS_PROMETHEUS}"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "thresholds"
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": null
+              },
+              {
+                "color": "yellow",
+                "value": 5
+              },
+              {
+                "color": "red",
+                "value": 10
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 4,
+        "w": 6,
+        "x": 0,
+        "y": 15
+      },
+      "id": 11,
+      "options": {
+        "colorMode": "value",
+        "graphMode": "area",
+        "justifyMode": "auto",
+        "orientation": "auto",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "",
+          "values": false
+        },
+        "textMode": "auto"
+      },
+      "pluginVersion": "10.0.0",
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "${DS_PROMETHEUS}"
+          },
+          "editorMode": "code",
+          "expr": "wordpress_cron_overdue_total",
+          "instant": true,
+          "legendFormat": "__auto",
+          "refId": "A"
+        }
+      ],
+      "title": "Overdue Cron Events",
+      "type": "stat"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "${DS_PROMETHEUS}"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "thresholds"
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "blue",
+                "value": null
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 4,
+        "w": 6,
+        "x": 6,
+        "y": 15
+      },
+      "id": 12,
+      "options": {
+        "colorMode": "value",
+        "graphMode": "none",
+        "justifyMode": "auto",
+        "orientation": "auto",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "",
+          "values": false
+        },
+        "textMode": "auto"
+      },
+      "pluginVersion": "10.0.0",
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "${DS_PROMETHEUS}"
+          },
+          "editorMode": "code",
+          "expr": "sum(wordpress_cron_events_total)",
+          "instant": true,
+          "legendFormat": "__auto",
+          "refId": "A"
+        }
+      ],
+      "title": "Total Cron Events",
+      "type": "stat"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "${DS_PROMETHEUS}"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "thresholds"
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "blue",
+                "value": null
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 4,
+        "w": 6,
+        "x": 12,
+        "y": 15
+      },
+      "id": 13,
+      "options": {
+        "colorMode": "value",
+        "graphMode": "none",
+        "justifyMode": "auto",
+        "orientation": "auto",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "",
+          "values": false
+        },
+        "textMode": "auto"
+      },
+      "pluginVersion": "10.0.0",
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "${DS_PROMETHEUS}"
+          },
+          "editorMode": "code",
+          "expr": "wordpress_transients_total{type=\"total\"}",
+          "instant": true,
+          "legendFormat": "__auto",
+          "refId": "A"
+        }
+      ],
+      "title": "Total Transients",
+      "type": "stat"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "${DS_PROMETHEUS}"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "thresholds"
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": null
+              },
+              {
+                "color": "yellow",
+                "value": 50
+              },
+              {
+                "color": "red",
+                "value": 100
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 4,
+        "w": 6,
+        "x": 18,
+        "y": 15
+      },
+      "id": 14,
+      "options": {
+        "colorMode": "value",
+        "graphMode": "area",
+        "justifyMode": "auto",
+        "orientation": "auto",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "",
+          "values": false
+        },
+        "textMode": "auto"
+      },
+      "pluginVersion": "10.0.0",
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "${DS_PROMETHEUS}"
+          },
+          "editorMode": "code",
+          "expr": "wordpress_transients_total{type=\"expired\"}",
+          "instant": true,
+          "legendFormat": "__auto",
+          "refId": "A"
+        }
+      ],
+      "title": "Expired Transients",
+      "type": "stat"
+    },
+    {
+      "datasource": {
+        "type": "prometheus",
+        "uid": "${DS_PROMETHEUS}"
+      },
+      "fieldConfig": {
+        "defaults": {
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "axisBorderShow": false,
+            "axisCenteredZero": false,
+            "axisColorMode": "text",
+            "axisLabel": "",
+            "axisPlacement": "auto",
+            "barAlignment": 0,
+            "drawStyle": "bars",
+            "fillOpacity": 80,
+            "gradientMode": "none",
+            "hideFrom": {
+              "legend": false,
+              "tooltip": false,
+              "viz": false
+            },
+            "insertNulls": false,
+            "lineInterpolation": "linear",
+            "lineWidth": 1,
+            "pointSize": 5,
+            "scaleDistribution": {
+              "type": "linear"
+            },
+            "showPoints": "auto",
+            "spanNulls": false,
+            "stacking": {
+              "group": "A",
+              "mode": "none"
+            },
+            "thresholdsStyle": {
+              "mode": "off"
+            }
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green",
+                "value": null
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "gridPos": {
+        "h": 8,
+        "w": 24,
+        "x": 0,
+        "y": 19
+      },
+      "id": 15,
+      "options": {
+        "legend": {
+          "calcs": [],
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true
+        },
+        "tooltip": {
+          "mode": "single",
+          "sort": "none"
+        }
+      },
+      "targets": [
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "${DS_PROMETHEUS}"
+          },
+          "editorMode": "code",
+          "expr": "topk(10, wordpress_cron_events_total)",
+          "instant": false,
+          "legendFormat": "{{hook}}",
+          "range": true,
+          "refId": "A"
+        }
+      ],
+      "title": "Top 10 Cron Hooks",
+      "type": "timeseries"
+    }
+  ],
+  "refresh": "30s",
+  "schemaVersion": 39,
+  "tags": ["wordpress", "prometheus"],
+  "templating": {
+    "list": [
+      {
+        "current": {
+          "selected": false,
+          "text": "Prometheus",
+          "value": "Prometheus"
+        },
+        "hide": 0,
+        "includeAll": false,
+        "label": "Data Source",
+        "multi": false,
+        "name": "DS_PROMETHEUS",
+        "options": [],
+        "query": "prometheus",
+        "queryValue": "",
+        "refresh": 1,
+        "regex": "",
+        "skipUrlSync": false,
+        "type": "datasource"
+      }
+    ]
+  },
+  "time": {
+    "from": "now-6h",
+    "to": "now"
+  },
+  "timepicker": {},
+  "timezone": "browser",
+  "title": "WordPress Overview",
+  "uid": "wp-prometheus-overview",
+  "version": 1,
+  "weekStart": ""
+}

assets/js/admin.js

@@ -7,7 +7,29 @@
 (function($) {
     'use strict';
 
+    var importFileContent = null;
+
     $(document).ready(function() {
+        // License tab handlers.
+        initLicenseHandlers();
+
+        // Custom metrics tab handlers.
+        initCustomMetricsHandlers();
+
+        // Dashboards tab handlers.
+        initDashboardsHandlers();
+
+        // Runtime metrics reset handler.
+        initResetRuntimeHandler();
+
+        // Storage tab handlers.
+        initStorageHandlers();
+    });
+
+    /**
+     * Initialize license tab handlers.
+     */
+    function initLicenseHandlers() {
         // Validate license button.
         $('#wp-prometheus-validate-license').on('click', function(e) {
             e.preventDefault();
@@ -23,11 +45,171 @@
         // Regenerate token button.
         $('#wp-prometheus-regenerate-token').on('click', function(e) {
             e.preventDefault();
-            if (confirm('Are you sure you want to regenerate the auth token? You will need to update your Prometheus configuration.')) {
+            if (confirm(wpPrometheus.confirmRegenerateToken)) {
                 var newToken = generateToken(32);
                 $('#wp_prometheus_auth_token').val(newToken);
             }
         });
+    }
+
+    /**
+     * Initialize custom metrics tab handlers.
+     */
+    function initCustomMetricsHandlers() {
+        var $formContainer = $('#wp-prometheus-metric-form-container');
+        var $form = $('#wp-prometheus-metric-form');
+        var $showFormBtn = $('#show-metric-form');
+
+        // Show metric form.
+        $showFormBtn.on('click', function() {
+            resetMetricForm();
+            $formContainer.slideDown();
+            $(this).hide();
+        });
+
+        // Cancel metric form.
+        $('#cancel-metric-form').on('click', function() {
+            $formContainer.slideUp();
+            $showFormBtn.show();
+            // Remove edit parameter from URL.
+            if (window.location.search.indexOf('edit=') > -1) {
+                window.history.pushState({}, '', window.location.pathname + '?page=wp-prometheus&tab=custom');
+            }
+        });
+
+        // Value type toggle.
+        $('input[name="value_type"]').on('change', function() {
+            var valueType = $(this).val();
+            if (valueType === 'option') {
+                $('#option-config-row').show();
+                $('#static-values-row').hide();
+            } else {
+                $('#option-config-row').hide();
+                $('#static-values-row').show();
+            }
+        });
+
+        // Add label.
+        $('#add-label').on('click', function() {
+            var $container = $('#metric-labels-container');
+            var labelCount = $container.find('.metric-label-row').length;
+
+            if (labelCount >= 5) {
+                alert('Maximum 5 labels allowed per metric.');
+                return;
+            }
+
+            var $row = $('<div class="metric-label-row">' +
+                '<input type="text" name="labels[]" class="regular-text" placeholder="label_name" pattern="[a-zA-Z_][a-zA-Z0-9_]*">' +
+                '<button type="button" class="button remove-label">&times;</button>' +
+                '</div>');
+            $container.append($row);
+            updateValueRows();
+        });
+
+        // Remove label.
+        $(document).on('click', '.remove-label', function() {
+            $(this).closest('.metric-label-row').remove();
+            updateValueRows();
+        });
+
+        // Add value row.
+        $('#add-value-row').on('click', function() {
+            var $container = $('#metric-values-container');
+            var rowCount = $container.find('.metric-value-row').length;
+            var labelCount = getLabelCount();
+
+            var $row = $('<div class="metric-value-row"></div>');
+
+            // Add label value inputs.
+            var labels = getLabels();
+            for (var i = 0; i < labelCount; i++) {
+                $row.append('<input type="text" name="label_values[' + rowCount + '][]" class="small-text" placeholder="' + (labels[i] || 'value') + '">');
+            }
+
+            // Add metric value input.
+            $row.append('<input type="number" name="label_values[' + rowCount + '][]" class="small-text" step="any" placeholder="Value">');
+            $row.append('<button type="button" class="button remove-value-row">&times;</button>');
+
+            $container.append($row);
+        });
+
+        // Remove value row.
+        $(document).on('click', '.remove-value-row', function() {
+            $(this).closest('.metric-value-row').remove();
+        });
+
+        // Submit metric form.
+        $form.on('submit', function(e) {
+            e.preventDefault();
+            saveCustomMetric();
+        });
+
+        // Delete metric.
+        $(document).on('click', '.delete-metric', function() {
+            var id = $(this).data('id');
+            if (confirm(wpPrometheus.confirmDelete)) {
+                deleteCustomMetric(id);
+            }
+        });
+
+        // Export metrics.
+        $('#export-metrics').on('click', function() {
+            exportMetrics();
+        });
+
+        // Import metrics - trigger file input.
+        $('#import-metrics-btn').on('click', function() {
+            $('#import-metrics-file').click();
+        });
+
+        // Import file selected.
+        $('#import-metrics-file').on('change', function(e) {
+            var file = e.target.files[0];
+            if (file) {
+                var reader = new FileReader();
+                reader.onload = function(e) {
+                    importFileContent = e.target.result;
+                    $('#import-options').slideDown();
+                };
+                reader.readAsText(file);
+            }
+        });
+
+        // Confirm import.
+        $('#confirm-import').on('click', function() {
+            var mode = $('input[name="import_mode"]:checked').val();
+            importMetrics(importFileContent, mode);
+        });
+
+        // Cancel import.
+        $('#cancel-import').on('click', function() {
+            $('#import-options').slideUp();
+            $('#import-metrics-file').val('');
+            importFileContent = null;
+        });
+    }
+
+    /**
+     * Initialize dashboards tab handlers.
+     */
+    function initDashboardsHandlers() {
+        $(document).on('click', '.download-dashboard', function() {
+            var slug = $(this).data('slug');
+            downloadDashboard(slug);
+        });
+    }
+
+    /**
+     * Initialize reset runtime metrics handler.
+     */
+    function initResetRuntimeHandler() {
+        $('#wp-prometheus-reset-runtime').on('click', function() {
+            if (confirm(wpPrometheus.confirmReset)) {
+                resetRuntimeMetrics();
+            }
+        });
+    }
 
     /**
      * Perform a license action via AJAX.
@@ -53,37 +235,323 @@
                 $spinner.removeClass('is-active');
 
                 if (response.success) {
-                        $message
-                            .removeClass('notice-error')
-                            .addClass('notice notice-success')
-                            .html('<p>' + response.data.message + '</p>')
-                            .show();
+                    showNotice($message, response.data.message, 'success');
 
                     // Reload page after successful validation/activation.
                     setTimeout(function() {
                         location.reload();
                     }, 1500);
                 } else {
-                        $message
-                            .removeClass('notice-success')
-                            .addClass('notice notice-error')
-                            .html('<p>' + (response.data.message || 'An error occurred.') + '</p>')
-                            .show();
+                    showNotice($message, response.data.message || 'An error occurred.', 'error');
                 }
             },
             error: function() {
                 $spinner.removeClass('is-active');
-                    $message
-                        .removeClass('notice-success')
-                        .addClass('notice notice-error')
-                        .html('<p>Connection error. Please try again.</p>')
-                        .show();
+                showNotice($message, 'Connection error. Please try again.', 'error');
             }
         });
     }
 
     /**
-         * Generate a random token.
+     * Save custom metric via AJAX.
+     */
+    function saveCustomMetric() {
+        var $spinner = $('#wp-prometheus-metric-spinner');
+        var $message = $('#wp-prometheus-metric-message');
+        var $form = $('#wp-prometheus-metric-form');
+
+        $spinner.addClass('is-active');
+        $message.hide();
+
+        var formData = $form.serialize();
+        formData += '&action=wp_prometheus_save_custom_metric';
+        formData += '&nonce=' + wpPrometheus.customMetricNonce;
+
+        $.ajax({
+            url: wpPrometheus.ajaxUrl,
+            type: 'POST',
+            data: formData,
+            success: function(response) {
+                $spinner.removeClass('is-active');
+
+                if (response.success) {
+                    showNotice($message, response.data.message, 'success');
+
+                    setTimeout(function() {
+                        window.location.href = window.location.pathname + '?page=wp-prometheus&tab=custom';
+                    }, 1000);
+                } else {
+                    showNotice($message, response.data.message || 'An error occurred.', 'error');
+                }
+            },
+            error: function() {
+                $spinner.removeClass('is-active');
+                showNotice($message, 'Connection error. Please try again.', 'error');
+            }
+        });
+    }
+
+    /**
+     * Delete custom metric via AJAX.
+     *
+     * @param {string} id Metric ID.
+     */
+    function deleteCustomMetric(id) {
+        $.ajax({
+            url: wpPrometheus.ajaxUrl,
+            type: 'POST',
+            data: {
+                action: 'wp_prometheus_delete_custom_metric',
+                nonce: wpPrometheus.customMetricNonce,
+                id: id
+            },
+            success: function(response) {
+                if (response.success) {
+                    $('tr[data-metric-id="' + id + '"]').fadeOut(function() {
+                        $(this).remove();
+                        // Check if table is empty.
+                        if ($('.wp-prometheus-custom-metrics tbody tr').length === 0) {
+                            location.reload();
+                        }
+                    });
+                } else {
+                    alert(response.data.message || 'An error occurred.');
+                }
+            },
+            error: function() {
+                alert('Connection error. Please try again.');
+            }
+        });
+    }
+
+    /**
+     * Export metrics via AJAX.
+     */
+    function exportMetrics() {
+        $.ajax({
+            url: wpPrometheus.ajaxUrl,
+            type: 'POST',
+            data: {
+                action: 'wp_prometheus_export_metrics',
+                nonce: wpPrometheus.exportNonce
+            },
+            success: function(response) {
+                if (response.success) {
+                    downloadFile(response.data.json, response.data.filename, 'application/json');
+                } else {
+                    alert(response.data.message || 'An error occurred.');
+                }
+            },
+            error: function() {
+                alert('Connection error. Please try again.');
+            }
+        });
+    }
+
+    /**
+     * Import metrics via AJAX.
+     *
+     * @param {string} json JSON content.
+     * @param {string} mode Import mode.
+     */
+    function importMetrics(json, mode) {
+        var $spinner = $('#wp-prometheus-import-spinner');
+        var $message = $('#wp-prometheus-import-message');
+
+        $spinner.addClass('is-active');
+        $message.hide();
+
+        $.ajax({
+            url: wpPrometheus.ajaxUrl,
+            type: 'POST',
+            data: {
+                action: 'wp_prometheus_import_metrics',
+                nonce: wpPrometheus.importNonce,
+                json: json,
+                mode: mode
+            },
+            success: function(response) {
+                $spinner.removeClass('is-active');
+
+                if (response.success) {
+                    showNotice($message, response.data.message, 'success');
+
+                    $('#import-options').slideUp();
+                    $('#import-metrics-file').val('');
+                    importFileContent = null;
+
+                    setTimeout(function() {
+                        location.reload();
+                    }, 1500);
+                } else {
+                    showNotice($message, response.data.message || 'An error occurred.', 'error');
+                }
+            },
+            error: function() {
+                $spinner.removeClass('is-active');
+                showNotice($message, 'Connection error. Please try again.', 'error');
+            }
+        });
+    }
+
+    /**
+     * Download dashboard via AJAX.
+     *
+     * @param {string} slug Dashboard slug.
+     */
+    function downloadDashboard(slug) {
+        $.ajax({
+            url: wpPrometheus.ajaxUrl,
+            type: 'POST',
+            data: {
+                action: 'wp_prometheus_download_dashboard',
+                nonce: wpPrometheus.dashboardNonce,
+                slug: slug
+            },
+            success: function(response) {
+                if (response.success) {
+                    downloadFile(response.data.json, response.data.filename, 'application/json');
+                } else {
+                    alert(response.data.message || 'An error occurred.');
+                }
+            },
+            error: function() {
+                alert('Connection error. Please try again.');
+            }
+        });
+    }
+
+    /**
+     * Reset runtime metrics via AJAX.
+     */
+    function resetRuntimeMetrics() {
+        var $spinner = $('#wp-prometheus-reset-spinner');
+        var $message = $('#wp-prometheus-reset-message');
+
+        $spinner.addClass('is-active');
+        $message.hide();
+
+        $.ajax({
+            url: wpPrometheus.ajaxUrl,
+            type: 'POST',
+            data: {
+                action: 'wp_prometheus_reset_runtime_metrics',
+                nonce: wpPrometheus.resetRuntimeNonce
+            },
+            success: function(response) {
+                $spinner.removeClass('is-active');
+
+                if (response.success) {
+                    showNotice($message, response.data.message, 'success');
+                } else {
+                    showNotice($message, response.data.message || 'An error occurred.', 'error');
+                }
+            },
+            error: function() {
+                $spinner.removeClass('is-active');
+                showNotice($message, 'Connection error. Please try again.', 'error');
+            }
+        });
+    }
+
+    /**
+     * Reset the metric form to default state.
+     */
+    function resetMetricForm() {
+        var $form = $('#wp-prometheus-metric-form');
+        $form[0].reset();
+        $('#metric-id').val('');
+        $('#wp-prometheus-form-title').text('Add New Metric');
+        $('#option-config-row').hide();
+        $('#static-values-row').show();
+        $('#wp-prometheus-metric-message').hide();
+
+        // Reset labels to single empty row.
+        $('#metric-labels-container').html(
+            '<div class="metric-label-row">' +
+            '<input type="text" name="labels[]" class="regular-text" placeholder="label_name" pattern="[a-zA-Z_][a-zA-Z0-9_]*">' +
+            '<button type="button" class="button remove-label">&times;</button>' +
+            '</div>'
+        );
+
+        // Reset values to single empty row.
+        $('#metric-values-container').html(
+            '<div class="metric-value-row">' +
+            '<input type="number" name="label_values[0][]" class="small-text" step="any" placeholder="Value">' +
+            '<button type="button" class="button remove-value-row">&times;</button>' +
+            '</div>'
+        );
+    }
+
+    /**
+     * Update value rows when labels change.
+     */
+    function updateValueRows() {
+        var labels = getLabels();
+        var labelCount = labels.length;
+
+        $('#metric-values-container .metric-value-row').each(function(rowIndex) {
+            var $row = $(this);
+            var inputs = $row.find('input').toArray();
+            var currentValues = inputs.map(function(input) { return input.value; });
+
+            // Remove all inputs except the value and button.
+            $row.find('input').remove();
+
+            // Re-add label inputs using safe DOM construction.
+            for (var i = 0; i < labelCount; i++) {
+                var val = currentValues[i] || '';
+                var $input = $('<input>', {
+                    type: 'text',
+                    name: 'label_values[' + rowIndex + '][]',
+                    'class': 'small-text',
+                    placeholder: labels[i] || 'value',
+                    value: val
+                });
+                $row.prepend($input);
+            }
+
+            // Re-add value input using safe DOM construction.
+            var metricVal = currentValues[currentValues.length - 1] || '';
+            var $valueInput = $('<input>', {
+                type: 'number',
+                name: 'label_values[' + rowIndex + '][]',
+                'class': 'small-text',
+                step: 'any',
+                placeholder: 'Value',
+                value: metricVal
+            });
+            $row.find('.remove-value-row').before($valueInput);
+        });
+    }
+
+    /**
+     * Get current label names.
+     *
+     * @return {string[]} Array of label names.
+     */
+    function getLabels() {
+        var labels = [];
+        $('#metric-labels-container input[name="labels[]"]').each(function() {
+            var val = $(this).val().trim();
+            if (val) {
+                labels.push(val);
+            }
+        });
+        return labels;
+    }
+
+    /**
+     * Get current label count.
+     *
+     * @return {number} Number of labels.
+     */
+    function getLabelCount() {
+        return getLabels().length;
+    }
+
+    /**
+     * Generate a cryptographically secure random token.
      *
      * @param {number} length Token length.
      * @return {string} Generated token.
@@ -91,10 +559,150 @@
     function generateToken(length) {
         var charset = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
         var token = '';
+        var randomValues = new Uint32Array(length);
+        window.crypto.getRandomValues(randomValues);
         for (var i = 0; i < length; i++) {
-                token += charset.charAt(Math.floor(Math.random() * charset.length));
+            token += charset.charAt(randomValues[i] % charset.length);
         }
         return token;
     }
+
+    /**
+     * Show a notice message safely (XSS-safe).
+     *
+     * @param {jQuery}  $element  The message container element.
+     * @param {string}  message   The message text.
+     * @param {string}  type      Notice type: 'success', 'error', or 'warning'.
+     */
+    function showNotice($element, message, type) {
+        var removeClasses = 'notice-error notice-success notice-warning';
+        $element
+            .removeClass(removeClasses)
+            .addClass('notice notice-' + type)
+            .empty()
+            .append($('<p>').text(message))
+            .show();
+    }
+
+    /**
+     * Download a file.
+     *
+     * @param {string} content File content.
+     * @param {string} filename Filename.
+     * @param {string} type MIME type.
+     */
+    function downloadFile(content, filename, type) {
+        var blob = new Blob([content], { type: type });
+        var url = URL.createObjectURL(blob);
+        var a = document.createElement('a');
+        a.href = url;
+        a.download = filename;
+        document.body.appendChild(a);
+        a.click();
+        document.body.removeChild(a);
+        URL.revokeObjectURL(url);
+    }
+
+    /**
+     * Initialize storage tab handlers.
+     */
+    function initStorageHandlers() {
+        var $form = $('#wp-prometheus-storage-form');
+        var $adapterSelect = $('#storage-adapter');
+
+        // Show/hide adapter-specific config.
+        $adapterSelect.on('change', function() {
+            var adapter = $(this).val();
+            $('#redis-config').toggle(adapter === 'redis');
+            $('#apcu-config').toggle(adapter === 'apcu');
         });
+
+        // Save storage settings.
+        $form.on('submit', function(e) {
+            e.preventDefault();
+            saveStorageSettings();
+        });
+
+        // Test storage connection.
+        $('#test-storage').on('click', function() {
+            testStorageConnection();
+        });
+    }
+
+    /**
+     * Save storage settings via AJAX.
+     */
+    function saveStorageSettings() {
+        var $spinner = $('#wp-prometheus-storage-spinner');
+        var $message = $('#wp-prometheus-storage-message');
+        var $form = $('#wp-prometheus-storage-form');
+
+        $spinner.addClass('is-active');
+        $message.hide();
+
+        var formData = $form.serialize();
+        formData += '&action=wp_prometheus_save_storage';
+        formData += '&nonce=' + wpPrometheus.storageNonce;
+
+        $.ajax({
+            url: wpPrometheus.ajaxUrl,
+            type: 'POST',
+            data: formData,
+            success: function(response) {
+                $spinner.removeClass('is-active');
+
+                if (response.success) {
+                    var type = response.data.warning ? 'warning' : 'success';
+                    showNotice($message, response.data.message, type);
+
+                    if (!response.data.warning) {
+                        setTimeout(function() {
+                            location.reload();
+                        }, 1500);
+                    }
+                } else {
+                    showNotice($message, response.data.message || 'An error occurred.', 'error');
+                }
+            },
+            error: function() {
+                $spinner.removeClass('is-active');
+                showNotice($message, 'Connection error. Please try again.', 'error');
+            }
+        });
+    }
+
+    /**
+     * Test storage connection via AJAX.
+     */
+    function testStorageConnection() {
+        var $spinner = $('#wp-prometheus-storage-spinner');
+        var $message = $('#wp-prometheus-storage-message');
+        var $form = $('#wp-prometheus-storage-form');
+
+        $spinner.addClass('is-active');
+        $message.hide();
+
+        var formData = $form.serialize();
+        formData += '&action=wp_prometheus_test_storage';
+        formData += '&nonce=' + wpPrometheus.storageNonce;
+
+        $.ajax({
+            url: wpPrometheus.ajaxUrl,
+            type: 'POST',
+            data: formData,
+            success: function(response) {
+                $spinner.removeClass('is-active');
+
+                if (response.success) {
+                    showNotice($message, response.data.message, 'success');
+                } else {
+                    showNotice($message, response.data.message || 'Connection test failed.', 'error');
+                }
+            },
+            error: function() {
+                $spinner.removeClass('is-active');
+                showNotice($message, 'Connection error. Please try again.', 'error');
+            }
+        });
+    }
 })(jQuery);

composer.json

@@ -32,6 +32,7 @@
         "promphp/prometheus_client_php": "^2.10"
     },
     "require-dev": {
+        "php-mock/php-mock-phpunit": "^2.10",
         "phpunit/phpunit": "^10.0",
         "squizlabs/php_codesniffer": "^3.7",
         "wp-coding-standards/wpcs": "^3.0",

composer.lock

@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "3cacd9c609c3c49fb4600d09a38c04be",
+    "content-hash": "cfd3853b3cf76d82f972f3326e4f94d3",
     "packages": [
         {
             "name": "magdev/wc-licensed-product-client",
@@ -1128,6 +1128,213 @@
             },
             "time": "2022-02-21T01:04:05+00:00"
         },
+        {
+            "name": "php-mock/php-mock",
+            "version": "2.7.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/php-mock/php-mock.git",
+                "reference": "b59734f19765296bb0311942850d02288a224890"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/php-mock/php-mock/zipball/b59734f19765296bb0311942850d02288a224890",
+                "reference": "b59734f19765296bb0311942850d02288a224890",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^5.6 || ^7.0 || ^8.0",
+                "phpunit/php-text-template": "^1 || ^2 || ^3 || ^4 || ^5 || ^6"
+            },
+            "replace": {
+                "malkusch/php-mock": "*"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "^5.7 || ^6.5 || ^7.5 || ^8.0 || ^9.0 || ^10.0 || ^11.0 || ^12.0 || ^13.0",
+                "squizlabs/php_codesniffer": "^3.8"
+            },
+            "suggest": {
+                "php-mock/php-mock-phpunit": "Allows integration into PHPUnit testcase with the trait PHPMock."
+            },
+            "type": "library",
+            "autoload": {
+                "files": [
+                    "autoload.php"
+                ],
+                "psr-4": {
+                    "phpmock\\": [
+                        "classes/",
+                        "tests/"
+                    ]
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "WTFPL"
+            ],
+            "authors": [
+                {
+                    "name": "Markus Malkusch",
+                    "email": "markus@malkusch.de",
+                    "homepage": "http://markus.malkusch.de",
+                    "role": "Developer"
+                }
+            ],
+            "description": "PHP-Mock can mock built-in PHP functions (e.g. time()). PHP-Mock relies on PHP's namespace fallback policy. No further extension is needed.",
+            "homepage": "https://github.com/php-mock/php-mock",
+            "keywords": [
+                "BDD",
+                "TDD",
+                "function",
+                "mock",
+                "stub",
+                "test",
+                "test double",
+                "testing"
+            ],
+            "support": {
+                "issues": "https://github.com/php-mock/php-mock/issues",
+                "source": "https://github.com/php-mock/php-mock/tree/2.7.0"
+            },
+            "funding": [
+                {
+                    "url": "https://github.com/michalbundyra",
+                    "type": "github"
+                }
+            ],
+            "time": "2026-02-06T07:39:37+00:00"
+        },
+        {
+            "name": "php-mock/php-mock-integration",
+            "version": "3.1.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/php-mock/php-mock-integration.git",
+                "reference": "cbbf39705ec13dece5b04133cef4e2fd3137a345"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/php-mock/php-mock-integration/zipball/cbbf39705ec13dece5b04133cef4e2fd3137a345",
+                "reference": "cbbf39705ec13dece5b04133cef4e2fd3137a345",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.6",
+                "php-mock/php-mock": "^2.5",
+                "phpunit/php-text-template": "^1 || ^2 || ^3 || ^4 || ^5 || ^6"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "^5.7.27 || ^6 || ^7 || ^8 || ^9 || ^10 || ^11 || ^12 || ^13"
+            },
+            "type": "library",
+            "autoload": {
+                "psr-4": {
+                    "phpmock\\integration\\": "classes/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "WTFPL"
+            ],
+            "authors": [
+                {
+                    "name": "Markus Malkusch",
+                    "email": "markus@malkusch.de",
+                    "homepage": "http://markus.malkusch.de",
+                    "role": "Developer"
+                }
+            ],
+            "description": "Integration package for PHP-Mock",
+            "homepage": "https://github.com/php-mock/php-mock-integration",
+            "keywords": [
+                "BDD",
+                "TDD",
+                "function",
+                "mock",
+                "stub",
+                "test",
+                "test double"
+            ],
+            "support": {
+                "issues": "https://github.com/php-mock/php-mock-integration/issues",
+                "source": "https://github.com/php-mock/php-mock-integration/tree/3.1.0"
+            },
+            "funding": [
+                {
+                    "url": "https://github.com/michalbundyra",
+                    "type": "github"
+                }
+            ],
+            "time": "2026-02-06T07:44:43+00:00"
+        },
+        {
+            "name": "php-mock/php-mock-phpunit",
+            "version": "2.15.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/php-mock/php-mock-phpunit.git",
+                "reference": "701df15b183f25af663af134eb71353cd838b955"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/php-mock/php-mock-phpunit/zipball/701df15b183f25af663af134eb71353cd838b955",
+                "reference": "701df15b183f25af663af134eb71353cd838b955",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=7",
+                "php-mock/php-mock-integration": "^3.0",
+                "phpunit/phpunit": "^6 || ^7 || ^8 || ^9 || ^10.0.17 || ^11 || ^12.0.9 || ^13"
+            },
+            "require-dev": {
+                "mockery/mockery": "^1.3.6"
+            },
+            "type": "library",
+            "autoload": {
+                "files": [
+                    "autoload.php"
+                ],
+                "psr-4": {
+                    "phpmock\\phpunit\\": "classes/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "WTFPL"
+            ],
+            "authors": [
+                {
+                    "name": "Markus Malkusch",
+                    "email": "markus@malkusch.de",
+                    "homepage": "http://markus.malkusch.de",
+                    "role": "Developer"
+                }
+            ],
+            "description": "Mock built-in PHP functions (e.g. time()) with PHPUnit. This package relies on PHP's namespace fallback policy. No further extension is needed.",
+            "homepage": "https://github.com/php-mock/php-mock-phpunit",
+            "keywords": [
+                "BDD",
+                "TDD",
+                "function",
+                "mock",
+                "phpunit",
+                "stub",
+                "test",
+                "test double",
+                "testing"
+            ],
+            "support": {
+                "issues": "https://github.com/php-mock/php-mock-phpunit/issues",
+                "source": "https://github.com/php-mock/php-mock-phpunit/tree/2.15.0"
+            },
+            "funding": [
+                {
+                    "url": "https://github.com/michalbundyra",
+                    "type": "github"
+                }
+            ],
+            "time": "2026-02-06T09:12:10+00:00"
+        },
         {
             "name": "phpcompatibility/php-compatibility",
             "version": "9.3.5",

phpunit.xml

@@ -0,0 +1,25 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
+         bootstrap="tests/bootstrap.php"
+         colors="true"
+         cacheDirectory=".phpunit.cache"
+         executionOrder="depends,defects"
+         beStrictAboutOutputDuringTests="true"
+         failOnRisky="true"
+         failOnWarning="true">
+    <testsuites>
+        <testsuite name="unit">
+            <directory>tests/Unit</directory>
+        </testsuite>
+    </testsuites>
+
+    <source>
+        <include>
+            <directory>src</directory>
+        </include>
+        <exclude>
+            <file>src/index.php</file>
+        </exclude>
+    </source>
+</phpunit>

src/Admin/DashboardProvider.php

@@ -0,0 +1,471 @@
+<?php
+/**
+ * Dashboard provider class.
+ *
+ * @package WP_Prometheus
+ */
+
+namespace Magdev\WpPrometheus\Admin;
+
+// Prevent direct file access.
+if ( ! defined( 'ABSPATH' ) ) {
+	exit;
+}
+
+/**
+ * DashboardProvider class.
+ *
+ * Provides Grafana dashboard templates for download.
+ * Supports both built-in dashboards and third-party registrations.
+ */
+class DashboardProvider {
+
+	/**
+	 * Dashboard directory path for built-in dashboards.
+	 *
+	 * @var string
+	 */
+	private string $dashboard_dir;
+
+	/**
+	 * Built-in dashboard definitions.
+	 *
+	 * @var array
+	 */
+	private array $builtin_dashboards = array();
+
+	/**
+	 * Third-party registered dashboard definitions.
+	 *
+	 * @var array
+	 */
+	private array $registered_dashboards = array();
+
+	/**
+	 * Whether the registration hook has been fired.
+	 *
+	 * @var bool
+	 */
+	private bool $hook_fired = false;
+
+	/**
+	 * Constructor.
+	 */
+	public function __construct() {
+		$this->dashboard_dir = WP_PROMETHEUS_PATH . 'assets/dashboards/';
+	}
+
+	/**
+	 * Get built-in dashboard definitions.
+	 *
+	 * Lazily initializes dashboard labels to avoid triggering textdomain loading
+	 * before the 'init' action (required since WordPress 6.7).
+	 *
+	 * @return array
+	 */
+	private function get_builtin_dashboards(): array {
+		if ( empty( $this->builtin_dashboards ) ) {
+			$this->builtin_dashboards = array(
+				'wordpress-overview'    => array(
+					'title'       => __( 'WordPress Overview', 'wp-prometheus' ),
+					'description' => __( 'General WordPress metrics including users, posts, comments, and plugins.', 'wp-prometheus' ),
+					'file'        => 'wordpress-overview.json',
+					'icon'        => 'dashicons-wordpress',
+					'source'      => 'builtin',
+				),
+				'wordpress-runtime'     => array(
+					'title'       => __( 'Runtime Performance', 'wp-prometheus' ),
+					'description' => __( 'HTTP request metrics, database query performance, and response times.', 'wp-prometheus' ),
+					'file'        => 'wordpress-runtime.json',
+					'icon'        => 'dashicons-performance',
+					'source'      => 'builtin',
+				),
+				'wordpress-woocommerce' => array(
+					'title'       => __( 'WooCommerce Store', 'wp-prometheus' ),
+					'description' => __( 'WooCommerce metrics including products, orders, revenue, and customers.', 'wp-prometheus' ),
+					'file'        => 'wordpress-woocommerce.json',
+					'icon'        => 'dashicons-cart',
+					'source'      => 'builtin',
+				),
+			);
+		}
+		return $this->builtin_dashboards;
+	}
+
+	/**
+	 * Register a third-party dashboard.
+	 *
+	 * @param string $slug Dashboard slug (unique identifier).
+	 * @param array  $args Dashboard configuration {
+	 *     @type string $title       Dashboard title (required).
+	 *     @type string $description Dashboard description.
+	 *     @type string $icon        Dashicon class (e.g., 'dashicons-chart-bar').
+	 *     @type string $file        Absolute path to JSON file (mutually exclusive with 'json').
+	 *     @type string $json        Inline JSON content (mutually exclusive with 'file').
+	 *     @type string $plugin      Plugin name for attribution.
+	 * }
+	 * @return bool True if registered successfully, false otherwise.
+	 */
+	public function register_dashboard( string $slug, array $args ): bool {
+		// Sanitize slug - must be valid identifier.
+		$slug = sanitize_key( $slug );
+
+		if ( empty( $slug ) ) {
+			if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+				// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+				error_log( 'WP Prometheus: Dashboard registration failed - invalid slug' );
+			}
+			return false;
+		}
+
+		// Check for duplicate slugs (built-in takes precedence).
+		if ( isset( $this->get_builtin_dashboards()[ $slug ] ) ) {
+			if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+				// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+				error_log( "WP Prometheus: Dashboard slug '$slug' conflicts with built-in dashboard" );
+			}
+			return false;
+		}
+
+		// Check for duplicate slugs in already registered dashboards.
+		if ( isset( $this->registered_dashboards[ $slug ] ) ) {
+			if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+				// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+				error_log( "WP Prometheus: Dashboard slug '$slug' already registered" );
+			}
+			return false;
+		}
+
+		// Validate required fields.
+		if ( empty( $args['title'] ) ) {
+			if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+				// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+				error_log( "WP Prometheus: Dashboard '$slug' missing required 'title'" );
+			}
+			return false;
+		}
+
+		// Must have either 'file' or 'json', not both.
+		$has_file = ! empty( $args['file'] );
+		$has_json = ! empty( $args['json'] );
+
+		if ( ! $has_file && ! $has_json ) {
+			if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+				// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+				error_log( "WP Prometheus: Dashboard '$slug' must have 'file' or 'json'" );
+			}
+			return false;
+		}
+
+		if ( $has_file && $has_json ) {
+			if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+				// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+				error_log( "WP Prometheus: Dashboard '$slug' cannot have both 'file' and 'json'" );
+			}
+			return false;
+		}
+
+		// Validate file path if provided.
+		if ( $has_file ) {
+			$file_path = $args['file'];
+
+			// Must be absolute path.
+			if ( ! path_is_absolute( $file_path ) ) {
+				if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+					// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+					error_log( "WP Prometheus: Dashboard '$slug' file path must be absolute" );
+				}
+				return false;
+			}
+
+			// File must exist and be readable.
+			if ( ! file_exists( $file_path ) || ! is_readable( $file_path ) ) {
+				if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+					// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+					error_log( "WP Prometheus: Dashboard '$slug' file not found: $file_path" );
+				}
+				return false;
+			}
+
+			// Security: Prevent path traversal - file must be under wp-content.
+			$real_path      = realpath( $file_path );
+			$wp_content_dir = realpath( WP_CONTENT_DIR );
+
+			if ( false === $real_path || false === $wp_content_dir ||
+				strpos( $real_path, $wp_content_dir ) !== 0 ) {
+				if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+					// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+					error_log( "WP Prometheus: Dashboard '$slug' file outside wp-content" );
+				}
+				return false;
+			}
+		}
+
+		// Validate JSON if provided inline.
+		if ( $has_json ) {
+			$decoded = json_decode( $args['json'], true );
+			if ( null === $decoded && json_last_error() !== JSON_ERROR_NONE ) {
+				if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+					// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+					error_log( "WP Prometheus: Dashboard '$slug' has invalid JSON" );
+				}
+				return false;
+			}
+		}
+
+		// Build dashboard entry.
+		$this->registered_dashboards[ $slug ] = array(
+			'title'       => sanitize_text_field( $args['title'] ),
+			'description' => sanitize_text_field( $args['description'] ?? '' ),
+			'icon'        => sanitize_html_class( $args['icon'] ?? 'dashicons-chart-line' ),
+			'file'        => $has_file ? $file_path : null,
+			'json'        => $has_json ? $args['json'] : null,
+			'plugin'      => sanitize_text_field( $args['plugin'] ?? '' ),
+			'source'      => 'third-party',
+		);
+
+		return true;
+	}
+
+	/**
+	 * Fire the dashboard registration hook with protection.
+	 *
+	 * @return void
+	 */
+	private function fire_registration_hook(): void {
+		if ( $this->hook_fired ) {
+			return;
+		}
+
+		$this->hook_fired = true;
+
+		// Check for isolated mode - skip third-party hooks.
+		$isolated_mode = defined( 'WP_PROMETHEUS_ISOLATED_MODE' ) && WP_PROMETHEUS_ISOLATED_MODE;
+
+		// Also check option for admin-side isolated mode.
+		if ( ! $isolated_mode ) {
+			$isolated_mode = (bool) get_option( 'wp_prometheus_isolated_mode', false );
+		}
+
+		if ( $isolated_mode ) {
+			return;
+		}
+
+		// Use output buffering to capture any accidental output.
+		ob_start();
+
+		try {
+			/**
+			 * Fires to allow third-party plugins to register dashboards.
+			 *
+			 * @since 0.4.6
+			 *
+			 * @param DashboardProvider $provider The dashboard provider instance.
+			 */
+			do_action( 'wp_prometheus_register_dashboards', $this );
+		} catch ( \Throwable $e ) {
+			if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+				// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+				error_log( 'WP Prometheus: Error in dashboard registration hook: ' . $e->getMessage() );
+			}
+		}
+
+		// Discard any output from plugins.
+		ob_end_clean();
+	}
+
+	/**
+	 * Get list of available dashboards.
+	 *
+	 * @return array
+	 */
+	public function get_available(): array {
+		// Fire registration hook first (only once).
+		$this->fire_registration_hook();
+
+		$available = array();
+
+		// Add built-in dashboards (check file exists).
+		foreach ( $this->get_builtin_dashboards() as $slug => $dashboard ) {
+			$file_path = $this->dashboard_dir . $dashboard['file'];
+			if ( file_exists( $file_path ) ) {
+				$available[ $slug ] = $dashboard;
+			}
+		}
+
+		// Add registered third-party dashboards.
+		foreach ( $this->registered_dashboards as $slug => $dashboard ) {
+			// Already validated during registration, but double-check.
+			if ( ! empty( $dashboard['json'] ) ||
+				( ! empty( $dashboard['file'] ) && file_exists( $dashboard['file'] ) ) ) {
+				$available[ $slug ] = $dashboard;
+			}
+		}
+
+		return $available;
+	}
+
+	/**
+	 * Get dashboard content by slug.
+	 *
+	 * @param string $slug Dashboard slug.
+	 * @return string|null JSON content or null if not found.
+	 */
+	public function get_dashboard( string $slug ): ?string {
+		// Fire registration hook first.
+		$this->fire_registration_hook();
+
+		// Validate slug.
+		$slug = sanitize_file_name( $slug );
+
+		// Check built-in dashboards first.
+		$builtin = $this->get_builtin_dashboards();
+		if ( isset( $builtin[ $slug ] ) ) {
+			$dashboard = $builtin[ $slug ];
+			$file_path = $this->dashboard_dir . $dashboard['file'];
+
+			// Security: Ensure file is within dashboard directory.
+			$real_path = realpath( $file_path );
+			$real_dir  = realpath( $this->dashboard_dir );
+
+			if ( false === $real_path || false === $real_dir ||
+				strpos( $real_path, $real_dir ) !== 0 ) {
+				return null;
+			}
+
+			if ( ! file_exists( $file_path ) || ! is_readable( $file_path ) ) {
+				return null;
+			}
+
+			// phpcs:ignore WordPress.WP.AlternativeFunctions.file_get_contents_file_get_contents
+			$content = file_get_contents( $file_path );
+
+			return false === $content ? null : $content;
+		}
+
+		// Check registered dashboards.
+		if ( isset( $this->registered_dashboards[ $slug ] ) ) {
+			$dashboard = $this->registered_dashboards[ $slug ];
+
+			// Inline JSON.
+			if ( ! empty( $dashboard['json'] ) ) {
+				return $dashboard['json'];
+			}
+
+			// File-based.
+			if ( ! empty( $dashboard['file'] ) ) {
+				$file_path = $dashboard['file'];
+
+				// Security: Re-verify file is under wp-content.
+				$real_path      = realpath( $file_path );
+				$wp_content_dir = realpath( WP_CONTENT_DIR );
+
+				if ( false === $real_path || false === $wp_content_dir ||
+					strpos( $real_path, $wp_content_dir ) !== 0 ) {
+					return null;
+				}
+
+				if ( ! file_exists( $file_path ) || ! is_readable( $file_path ) ) {
+					return null;
+				}
+
+				// phpcs:ignore WordPress.WP.AlternativeFunctions.file_get_contents_file_get_contents
+				$content = file_get_contents( $file_path );
+
+				return false === $content ? null : $content;
+			}
+		}
+
+		return null;
+	}
+
+	/**
+	 * Get dashboard metadata by slug.
+	 *
+	 * @param string $slug Dashboard slug.
+	 * @return array|null Dashboard metadata or null if not found.
+	 */
+	public function get_metadata( string $slug ): ?array {
+		// Fire registration hook first.
+		$this->fire_registration_hook();
+
+		$slug = sanitize_file_name( $slug );
+
+		$builtin = $this->get_builtin_dashboards();
+		if ( isset( $builtin[ $slug ] ) ) {
+			return $builtin[ $slug ];
+		}
+
+		if ( isset( $this->registered_dashboards[ $slug ] ) ) {
+			return $this->registered_dashboards[ $slug ];
+		}
+
+		return null;
+	}
+
+	/**
+	 * Get filename for download.
+	 *
+	 * @param string $slug Dashboard slug.
+	 * @return string|null Filename or null if not found.
+	 */
+	public function get_filename( string $slug ): ?string {
+		// Fire registration hook first.
+		$this->fire_registration_hook();
+
+		$slug = sanitize_file_name( $slug );
+
+		// Built-in dashboards have predefined filenames.
+		$builtin = $this->get_builtin_dashboards();
+		if ( isset( $builtin[ $slug ] ) ) {
+			return $builtin[ $slug ]['file'];
+		}
+
+		// Registered dashboards - use file basename or generate from slug.
+		if ( isset( $this->registered_dashboards[ $slug ] ) ) {
+			$dashboard = $this->registered_dashboards[ $slug ];
+
+			if ( ! empty( $dashboard['file'] ) ) {
+				return basename( $dashboard['file'] );
+			}
+
+			// Generate filename from slug for inline JSON.
+			return $slug . '.json';
+		}
+
+		return null;
+	}
+
+	/**
+	 * Check if a dashboard is from a third-party plugin.
+	 *
+	 * @param string $slug Dashboard slug.
+	 * @return bool True if third-party, false if built-in or not found.
+	 */
+	public function is_third_party( string $slug ): bool {
+		$this->fire_registration_hook();
+
+		$slug = sanitize_file_name( $slug );
+
+		return isset( $this->registered_dashboards[ $slug ] );
+	}
+
+	/**
+	 * Get the plugin name for a third-party dashboard.
+	 *
+	 * @param string $slug Dashboard slug.
+	 * @return string|null Plugin name or null if not found/built-in.
+	 */
+	public function get_plugin_name( string $slug ): ?string {
+		$this->fire_registration_hook();
+
+		$slug = sanitize_file_name( $slug );
+
+		if ( isset( $this->registered_dashboards[ $slug ] ) ) {
+			$plugin = $this->registered_dashboards[ $slug ]['plugin'];
+			return ! empty( $plugin ) ? $plugin : null;
+		}
+
+		return null;
+	}
+}

src/Endpoint/MetricsEndpoint.php

@@ -45,7 +45,9 @@ class MetricsEndpoint {
      */
     private function init_hooks(): void {
         add_action( 'init', array( $this, 'register_endpoint' ) );
-        add_action( 'template_redirect', array( $this, 'handle_request' ) );
+        // Use parse_request instead of template_redirect to handle the request early,
+        // before themes and other plugins (like Twig-based ones) can interfere.
+        add_action( 'parse_request', array( $this, 'handle_request' ) );
     }
 
     /**
@@ -66,10 +68,13 @@ class MetricsEndpoint {
     /**
      * Handle the metrics endpoint request.
      *
+     * Called during parse_request to intercept before themes/plugins load.
+     *
+     * @param \WP $wp WordPress environment instance.
      * @return void
      */
-    public function handle_request(): void {
-        if ( ! get_query_var( 'wp_prometheus_metrics' ) ) {
+    public function handle_request( \WP $wp ): void {
+        if ( empty( $wp->query_vars['wp_prometheus_metrics'] ) ) {
             return;
         }
 
@@ -97,52 +102,12 @@ class MetricsEndpoint {
     /**
      * Authenticate the metrics request.
      *
+     * Uses the shared authentication helper to avoid code duplication
+     * with the isolated mode handler in wp-prometheus.php.
+     *
      * @return bool
      */
     private function authenticate(): bool {
-        $auth_token = get_option( 'wp_prometheus_auth_token', '' );
-
-        // If no token is set, deny access.
-        if ( empty( $auth_token ) ) {
-            return false;
-        }
-
-        // Check for Bearer token in Authorization header.
-        $auth_header = $this->get_authorization_header();
-        if ( ! empty( $auth_header ) && preg_match( '/Bearer\s+(.*)$/i', $auth_header, $matches ) ) {
-            return hash_equals( $auth_token, $matches[1] );
-        }
-
-        // Check for token in query parameter (less secure but useful for testing).
-        // phpcs:ignore WordPress.Security.NonceVerification.Recommended -- Auth token check.
-        if ( isset( $_GET['token'] ) && hash_equals( $auth_token, sanitize_text_field( wp_unslash( $_GET['token'] ) ) ) ) {
-            return true;
-        }
-
-        return false;
-    }
-
-    /**
-     * Get the Authorization header from the request.
-     *
-     * @return string
-     */
-    private function get_authorization_header(): string {
-        if ( isset( $_SERVER['HTTP_AUTHORIZATION'] ) ) {
-            return sanitize_text_field( wp_unslash( $_SERVER['HTTP_AUTHORIZATION'] ) );
-        }
-
-        if ( isset( $_SERVER['REDIRECT_HTTP_AUTHORIZATION'] ) ) {
-            return sanitize_text_field( wp_unslash( $_SERVER['REDIRECT_HTTP_AUTHORIZATION'] ) );
-        }
-
-        if ( function_exists( 'apache_request_headers' ) ) {
-            $headers = apache_request_headers();
-            if ( isset( $headers['Authorization'] ) ) {
-                return sanitize_text_field( $headers['Authorization'] );
-            }
-        }
-
-        return '';
+        return wp_prometheus_authenticate_request();
     }
 }

src/Installer.php

@@ -64,6 +64,15 @@ final class Installer {
             'wp_prometheus_enable_default_metrics',
             'wp_prometheus_enabled_metrics',
             'wp_prometheus_runtime_metrics',
+            'wp_prometheus_custom_metrics',
+            'wp_prometheus_isolated_mode',
+            'wp_prometheus_storage_adapter',
+            'wp_prometheus_redis_host',
+            'wp_prometheus_redis_port',
+            'wp_prometheus_redis_password',
+            'wp_prometheus_redis_database',
+            'wp_prometheus_redis_prefix',
+            'wp_prometheus_apcu_prefix',
         );
 
         foreach ( $options as $option ) {

src/License/Manager.php

@@ -302,37 +302,113 @@ final class Manager {
      * @return bool
      */
     public static function is_license_valid(): bool {
+        // Bypass license check on localhost for development.
+        if ( self::is_localhost() ) {
+            return true;
+        }
+
         $status = get_option( self::OPTION_LICENSE_STATUS, 'unchecked' );
         return 'valid' === $status;
     }
 
+    /**
+     * Check if the current site is running on localhost.
+     *
+     * @return bool
+     */
+    public static function is_localhost(): bool {
+        $host = wp_parse_url( home_url(), PHP_URL_HOST );
+
+        $localhost_patterns = array(
+            'localhost',
+            '127.0.0.1',
+            '::1',
+        );
+
+        // Check exact matches.
+        if ( in_array( $host, $localhost_patterns, true ) ) {
+            return true;
+        }
+
+        // Check .localhost TLD (e.g., mysite.localhost).
+        if ( str_ends_with( $host, '.localhost' ) ) {
+            return true;
+        }
+
+        // Check .local TLD (common for local development).
+        if ( str_ends_with( $host, '.local' ) ) {
+            return true;
+        }
+
+        return false;
+    }
+
     /**
      * Get the license key.
      *
+     * Environment variable WP_PROMETHEUS_LICENSE_KEY takes precedence.
+     *
      * @return string
      */
     public static function get_license_key(): string {
+        $env = getenv( 'WP_PROMETHEUS_LICENSE_KEY' );
+        if ( false !== $env && '' !== $env ) {
+            return $env;
+        }
         return get_option( self::OPTION_LICENSE_KEY, '' );
     }
 
     /**
      * Get the license server URL.
      *
+     * Environment variable WP_PROMETHEUS_LICENSE_SERVER_URL takes precedence.
+     *
      * @return string
      */
     public static function get_server_url(): string {
+        $env = getenv( 'WP_PROMETHEUS_LICENSE_SERVER_URL' );
+        if ( false !== $env && '' !== $env ) {
+            return $env;
+        }
         return get_option( self::OPTION_SERVER_URL, '' );
     }
 
     /**
      * Get the server secret.
      *
+     * Environment variable WP_PROMETHEUS_LICENSE_SERVER_SECRET takes precedence.
+     *
      * @return string
      */
     public static function get_server_secret(): string {
+        $env = getenv( 'WP_PROMETHEUS_LICENSE_SERVER_SECRET' );
+        if ( false !== $env && '' !== $env ) {
+            return $env;
+        }
         return get_option( self::OPTION_SERVER_SECRET, '' );
     }
 
+    /**
+     * Check if a license setting is overridden by an environment variable.
+     *
+     * @param string $setting One of 'server_url', 'license_key', 'server_secret'.
+     * @return bool
+     */
+    public static function is_env_override( string $setting ): bool {
+        $map = array(
+            'server_url'    => 'WP_PROMETHEUS_LICENSE_SERVER_URL',
+            'license_key'   => 'WP_PROMETHEUS_LICENSE_KEY',
+            'server_secret' => 'WP_PROMETHEUS_LICENSE_SERVER_SECRET',
+        );
+
+        if ( ! isset( $map[ $setting ] ) ) {
+            return false;
+        }
+
+        $env = getenv( $map[ $setting ] );
+        return false !== $env && '' !== $env;
+    }
+
     /**
      * Get cached license status.
      *
@@ -396,9 +472,16 @@ final class Manager {
      * @return void
      */
     private function update_cached_status( string $status, array $data = array() ): void {
+        $previous_status = get_option( self::OPTION_LICENSE_STATUS, 'unchecked' );
+
         update_option( self::OPTION_LICENSE_STATUS, $status );
         update_option( self::OPTION_LICENSE_DATA, $data );
         update_option( self::OPTION_LAST_CHECK, time() );
+
+        // Flush rewrite rules when license becomes valid to register the /metrics endpoint.
+        if ( 'valid' === $status && 'valid' !== $previous_status ) {
+            flush_rewrite_rules();
+        }
     }
 
     /**
@@ -465,6 +548,9 @@ final class Manager {
         update_option( self::OPTION_LICENSE_DATA, array() );
         delete_transient( self::TRANSIENT_LICENSE_CHECK );
 
+        // Flush rewrite rules to remove the /metrics endpoint.
+        flush_rewrite_rules();
+
         wp_send_json_success( array(
             'success' => true,
             'message' => __( 'License deactivated.', 'wp-prometheus' ),

src/Metrics/Collector.php

@@ -8,8 +8,9 @@
 namespace Magdev\WpPrometheus\Metrics;
 
 use Prometheus\CollectorRegistry;
-use Prometheus\Storage\InMemory;
 use Prometheus\RenderTextFormat;
+use Magdev\WpPrometheus\Metrics\CustomMetricBuilder;
+use Magdev\WpPrometheus\Metrics\StorageFactory;
 
 // Prevent direct file access.
 if ( ! defined( 'ABSPATH' ) ) {
@@ -41,7 +42,7 @@ class Collector {
      * Constructor.
      */
     public function __construct() {
-        $this->registry = new CollectorRegistry( new InMemory() );
+        $this->registry = new CollectorRegistry( StorageFactory::get_adapter() );
     }
 
     /**
@@ -95,15 +96,87 @@ class Collector {
             $this->collect_plugins_total();
         }
 
+        // Collect cron metrics.
+        if ( in_array( 'wordpress_cron_events_total', $enabled_metrics, true ) ) {
+            $this->collect_cron_metrics();
+        }
+
+        // Collect transient metrics.
+        if ( in_array( 'wordpress_transients_total', $enabled_metrics, true ) ) {
+            $this->collect_transient_metrics();
+        }
+
+        // Collect WooCommerce metrics (if WooCommerce is active).
+        if ( $this->is_woocommerce_active() ) {
+            $this->collect_woocommerce_metrics( $enabled_metrics );
+        }
+
         // Collect runtime metrics (HTTP requests, DB queries).
         $this->collect_runtime_metrics( $enabled_metrics );
 
+        // Collect custom user-defined metrics.
+        $custom_builder = new CustomMetricBuilder();
+        $custom_builder->register_with_collector( $this );
+
         /**
          * Fires after default metrics are collected.
          *
+         * In isolated mode, skip custom hooks to avoid any potential issues.
+         * In safe mode (default), fire hooks with protection against recursion.
+         *
+         * @param Collector $collector The metrics collector instance.
+         */
+        if ( defined( 'WP_PROMETHEUS_ISOLATED_MODE' ) && WP_PROMETHEUS_ISOLATED_MODE ) {
+            // Isolated mode: skip all third-party hooks for maximum safety.
+            return;
+        }
+
+        // Safe mode: fire custom hooks with protection.
+        $this->fire_custom_metrics_hook();
+    }
+
+    /**
+     * Fire custom metrics hook with protection against recursion.
+     *
+     * Removes potentially problematic filters, uses output buffering,
+     * and catches any errors from third-party plugins.
+     *
+     * @return void
+     */
+    private function fire_custom_metrics_hook(): void {
+        // Remove content filters again (in case any plugin re-added them).
+        if ( function_exists( 'wp_prometheus_remove_content_filters' ) ) {
+            wp_prometheus_remove_content_filters();
+        } else {
+            // Fallback if function doesn't exist.
+            remove_all_filters( 'the_content' );
+            remove_all_filters( 'the_excerpt' );
+            remove_all_filters( 'get_the_excerpt' );
+            remove_all_filters( 'the_title' );
+        }
+
+        // Use output buffering to prevent any accidental output from plugins.
+        ob_start();
+
+        try {
+            /**
+             * Fires after default metrics are collected.
+             *
+             * Third-party plugins can use this hook to add custom metrics.
+             *
              * @param Collector $collector The metrics collector instance.
              */
             do_action( 'wp_prometheus_collect_metrics', $this );
+        } catch ( \Throwable $e ) {
+            // Log the error but don't let it break metrics output.
+            if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+                // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+                error_log( 'WP Prometheus: Error in custom metrics hook: ' . $e->getMessage() );
+            }
+        }
+
+        // Discard any output from plugins.
+        ob_end_clean();
     }
 
     /**
@@ -236,6 +309,385 @@ class Collector {
         $gauge->set( count( $all_plugins ) - count( $active_plugins ), array( 'inactive' ) );
     }
 
+    /**
+     * Collect cron metrics.
+     *
+     * @return void
+     */
+    private function collect_cron_metrics(): void {
+        $cron_array = _get_cron_array();
+
+        if ( ! is_array( $cron_array ) ) {
+            return;
+        }
+
+        // Events total gauge.
+        $events_gauge = $this->registry->getOrRegisterGauge(
+            $this->namespace,
+            'cron_events_total',
+            'Total number of scheduled cron events',
+            array( 'hook' )
+        );
+
+        // Count events by hook.
+        $hook_counts   = array();
+        $total_events  = 0;
+        $overdue_count = 0;
+        $current_time  = time();
+        $next_run      = PHP_INT_MAX;
+
+        foreach ( $cron_array as $timestamp => $cron ) {
+            if ( $timestamp < $next_run ) {
+                $next_run = $timestamp;
+            }
+
+            foreach ( $cron as $hook => $events ) {
+                $event_count = count( $events );
+                $total_events += $event_count;
+
+                if ( ! isset( $hook_counts[ $hook ] ) ) {
+                    $hook_counts[ $hook ] = 0;
+                }
+                $hook_counts[ $hook ] += $event_count;
+
+                // Check if overdue.
+                if ( $timestamp < $current_time ) {
+                    $overdue_count += $event_count;
+                }
+            }
+        }
+
+        // Set events by hook (limit to top 20 to avoid cardinality explosion).
+        arsort( $hook_counts );
+        $hook_counts = array_slice( $hook_counts, 0, 20, true );
+        foreach ( $hook_counts as $hook => $count ) {
+            $events_gauge->set( $count, array( $hook ) );
+        }
+
+        // Overdue events gauge.
+        $overdue_gauge = $this->registry->getOrRegisterGauge(
+            $this->namespace,
+            'cron_overdue_total',
+            'Number of overdue cron events',
+            array()
+        );
+        $overdue_gauge->set( $overdue_count, array() );
+
+        // Next run timestamp.
+        $next_run_gauge = $this->registry->getOrRegisterGauge(
+            $this->namespace,
+            'cron_next_run_timestamp',
+            'Unix timestamp of next scheduled cron event',
+            array()
+        );
+        if ( $next_run !== PHP_INT_MAX ) {
+            $next_run_gauge->set( $next_run, array() );
+        }
+    }
+
+    /**
+     * Collect transient metrics.
+     *
+     * @return void
+     */
+    private function collect_transient_metrics(): void {
+        global $wpdb;
+
+        // Count all transients.
+        // phpcs:ignore WordPress.DB.DirectDatabaseQuery
+        $transient_count = $wpdb->get_var(
+            "SELECT COUNT(*) FROM {$wpdb->options} WHERE option_name LIKE '_transient_%' AND option_name NOT LIKE '_transient_timeout_%'"
+        );
+
+        // Count transients with expiration.
+        // phpcs:ignore WordPress.DB.DirectDatabaseQuery
+        $expiring_count = $wpdb->get_var(
+            "SELECT COUNT(*) FROM {$wpdb->options} WHERE option_name LIKE '_transient_timeout_%'"
+        );
+
+        // Count expired transients.
+        // phpcs:ignore WordPress.DB.DirectDatabaseQuery
+        $expired_count = $wpdb->get_var(
+            $wpdb->prepare(
+                "SELECT COUNT(*) FROM {$wpdb->options} WHERE option_name LIKE '_transient_timeout_%%' AND option_value < %d",
+                time()
+            )
+        );
+
+        // Transients total gauge.
+        $transients_gauge = $this->registry->getOrRegisterGauge(
+            $this->namespace,
+            'transients_total',
+            'Total number of transients in database',
+            array( 'type' )
+        );
+
+        $transients_gauge->set( (int) $transient_count, array( 'total' ) );
+        $transients_gauge->set( (int) $expiring_count, array( 'with_expiration' ) );
+        $transients_gauge->set( (int) $transient_count - (int) $expiring_count, array( 'persistent' ) );
+        $transients_gauge->set( (int) $expired_count, array( 'expired' ) );
+
+        // Site transients (for multisite).
+        if ( is_multisite() ) {
+            // phpcs:ignore WordPress.DB.DirectDatabaseQuery
+            $site_transient_count = $wpdb->get_var(
+                "SELECT COUNT(*) FROM {$wpdb->sitemeta} WHERE meta_key LIKE '_site_transient_%' AND meta_key NOT LIKE '_site_transient_timeout_%'"
+            );
+
+            $transients_gauge->set( (int) $site_transient_count, array( 'site_transients' ) );
+        }
+    }
+
+    /**
+     * Check if WooCommerce is active.
+     *
+     * @return bool
+     */
+    private function is_woocommerce_active(): bool {
+        return class_exists( 'WooCommerce' );
+    }
+
+    /**
+     * Check if WooCommerce HPOS (High-Performance Order Storage) is enabled.
+     *
+     * @return bool
+     */
+    private function is_hpos_enabled(): bool {
+        return class_exists( '\Automattic\WooCommerce\Utilities\OrderUtil' )
+            && \Automattic\WooCommerce\Utilities\OrderUtil::custom_orders_table_usage_is_enabled();
+    }
+
+    /**
+     * Collect WooCommerce metrics.
+     *
+     * @param array $enabled_metrics List of enabled metrics.
+     * @return void
+     */
+    private function collect_woocommerce_metrics( array $enabled_metrics ): void {
+        // Products total.
+        if ( in_array( 'wordpress_woocommerce_products_total', $enabled_metrics, true ) ) {
+            $this->collect_woocommerce_products();
+        }
+
+        // Orders total.
+        if ( in_array( 'wordpress_woocommerce_orders_total', $enabled_metrics, true ) ) {
+            $this->collect_woocommerce_orders();
+        }
+
+        // Revenue.
+        if ( in_array( 'wordpress_woocommerce_revenue_total', $enabled_metrics, true ) ) {
+            $this->collect_woocommerce_revenue();
+        }
+
+        // Customers.
+        if ( in_array( 'wordpress_woocommerce_customers_total', $enabled_metrics, true ) ) {
+            $this->collect_woocommerce_customers();
+        }
+    }
+
+    /**
+     * Collect WooCommerce products metrics.
+     *
+     * @return void
+     */
+    private function collect_woocommerce_products(): void {
+        $gauge = $this->registry->getOrRegisterGauge(
+            $this->namespace,
+            'woocommerce_products_total',
+            'Total number of WooCommerce products by status and type',
+            array( 'status', 'type' )
+        );
+
+        // Get product counts by status.
+        $product_counts = wp_count_posts( 'product' );
+        $product_types  = wc_get_product_types();
+
+        foreach ( get_object_vars( $product_counts ) as $status => $count ) {
+            if ( (int) $count > 0 ) {
+                $gauge->set( (int) $count, array( $status, 'all' ) );
+            }
+        }
+
+        // Count by product type (for published products only) using count query.
+        foreach ( array_keys( $product_types ) as $type ) {
+            $args = array(
+                'status' => 'publish',
+                'type'   => $type,
+                'limit'  => 1,
+                'return' => 'ids',
+                'paginate' => true,
+            );
+            $result = wc_get_products( $args );
+            $gauge->set( $result->total, array( 'publish', $type ) );
+        }
+    }
+
+    /**
+     * Collect WooCommerce orders metrics.
+     *
+     * @return void
+     */
+    private function collect_woocommerce_orders(): void {
+        $gauge = $this->registry->getOrRegisterGauge(
+            $this->namespace,
+            'woocommerce_orders_total',
+            'Total number of WooCommerce orders by status',
+            array( 'status' )
+        );
+
+        // Get all registered order statuses and count each.
+        $statuses = wc_get_order_statuses();
+
+        foreach ( array_keys( $statuses ) as $status ) {
+            // Remove 'wc-' prefix for the label.
+            $status_label = str_replace( 'wc-', '', $status );
+            $count        = wc_orders_count( $status );
+            $gauge->set( (int) $count, array( $status_label ) );
+        }
+    }
+
+    /**
+     * Collect WooCommerce revenue metrics.
+     *
+     * @return void
+     */
+    private function collect_woocommerce_revenue(): void {
+        global $wpdb;
+
+        $gauge = $this->registry->getOrRegisterGauge(
+            $this->namespace,
+            'woocommerce_revenue_total',
+            'Total WooCommerce revenue',
+            array( 'period', 'currency' )
+        );
+
+        $currency = get_woocommerce_currency();
+
+        // Check if HPOS (High-Performance Order Storage) is enabled.
+        $hpos_enabled = $this->is_hpos_enabled();
+
+        if ( $hpos_enabled ) {
+            $orders_table = $wpdb->prefix . 'wc_orders';
+
+            // Total revenue (all time) - completed and processing orders.
+            // phpcs:ignore WordPress.DB.DirectDatabaseQuery
+            $total_revenue = $wpdb->get_var(
+                "SELECT SUM(total_amount) FROM {$orders_table} WHERE status IN ('wc-completed', 'wc-processing')"
+            );
+
+            // Today's revenue.
+            // phpcs:ignore WordPress.DB.DirectDatabaseQuery
+            $today_revenue = $wpdb->get_var(
+                $wpdb->prepare(
+                    "SELECT SUM(total_amount) FROM {$orders_table} WHERE status IN ('wc-completed', 'wc-processing') AND DATE(date_created_gmt) = %s",
+                    gmdate( 'Y-m-d' )
+                )
+            );
+
+            // This month's revenue.
+            // phpcs:ignore WordPress.DB.DirectDatabaseQuery
+            $month_revenue = $wpdb->get_var(
+                $wpdb->prepare(
+                    "SELECT SUM(total_amount) FROM {$orders_table} WHERE status IN ('wc-completed', 'wc-processing') AND YEAR(date_created_gmt) = %d AND MONTH(date_created_gmt) = %d",
+                    gmdate( 'Y' ),
+                    gmdate( 'm' )
+                )
+            );
+        } else {
+            // Legacy post-based orders.
+            // phpcs:ignore WordPress.DB.DirectDatabaseQuery
+            $total_revenue = $wpdb->get_var(
+                "SELECT SUM(meta_value) FROM {$wpdb->postmeta} pm
+                JOIN {$wpdb->posts} p ON p.ID = pm.post_id
+                WHERE pm.meta_key = '_order_total'
+                AND p.post_type = 'shop_order'
+                AND p.post_status IN ('wc-completed', 'wc-processing')"
+            );
+
+            // Today's revenue.
+            // phpcs:ignore WordPress.DB.DirectDatabaseQuery
+            $today_revenue = $wpdb->get_var(
+                $wpdb->prepare(
+                    "SELECT SUM(meta_value) FROM {$wpdb->postmeta} pm
+                    JOIN {$wpdb->posts} p ON p.ID = pm.post_id
+                    WHERE pm.meta_key = '_order_total'
+                    AND p.post_type = 'shop_order'
+                    AND p.post_status IN ('wc-completed', 'wc-processing')
+                    AND DATE(p.post_date_gmt) = %s",
+                    gmdate( 'Y-m-d' )
+                )
+            );
+
+            // This month's revenue.
+            // phpcs:ignore WordPress.DB.DirectDatabaseQuery
+            $month_revenue = $wpdb->get_var(
+                $wpdb->prepare(
+                    "SELECT SUM(meta_value) FROM {$wpdb->postmeta} pm
+                    JOIN {$wpdb->posts} p ON p.ID = pm.post_id
+                    WHERE pm.meta_key = '_order_total'
+                    AND p.post_type = 'shop_order'
+                    AND p.post_status IN ('wc-completed', 'wc-processing')
+                    AND YEAR(p.post_date_gmt) = %d
+                    AND MONTH(p.post_date_gmt) = %d",
+                    gmdate( 'Y' ),
+                    gmdate( 'm' )
+                )
+            );
+        }
+
+        $gauge->set( (float) ( $total_revenue ?? 0 ), array( 'all_time', $currency ) );
+        $gauge->set( (float) ( $today_revenue ?? 0 ), array( 'today', $currency ) );
+        $gauge->set( (float) ( $month_revenue ?? 0 ), array( 'month', $currency ) );
+    }
+
+    /**
+     * Collect WooCommerce customers metrics.
+     *
+     * @return void
+     */
+    private function collect_woocommerce_customers(): void {
+        $gauge = $this->registry->getOrRegisterGauge(
+            $this->namespace,
+            'woocommerce_customers_total',
+            'Total number of WooCommerce customers',
+            array( 'type' )
+        );
+
+        // Count users with customer role.
+        $customer_count = count_users();
+        $customers      = $customer_count['avail_roles']['customer'] ?? 0;
+
+        $gauge->set( $customers, array( 'registered' ) );
+
+        // Count guest orders (orders without user_id).
+        global $wpdb;
+
+        // Check if HPOS is enabled.
+        $hpos_enabled = class_exists( '\Automattic\WooCommerce\Utilities\OrderUtil' )
+            && \Automattic\WooCommerce\Utilities\OrderUtil::custom_orders_table_usage_is_enabled();
+
+        if ( $hpos_enabled ) {
+            $orders_table = $wpdb->prefix . 'wc_orders';
+
+            // phpcs:ignore WordPress.DB.DirectDatabaseQuery
+            $guest_orders = $wpdb->get_var(
+                "SELECT COUNT(DISTINCT billing_email) FROM {$orders_table} WHERE customer_id = 0 AND billing_email != ''"
+            );
+        } else {
+            // phpcs:ignore WordPress.DB.DirectDatabaseQuery
+            $guest_orders = $wpdb->get_var(
+                "SELECT COUNT(DISTINCT pm.meta_value) FROM {$wpdb->postmeta} pm
+                JOIN {$wpdb->posts} p ON p.ID = pm.post_id
+                LEFT JOIN {$wpdb->postmeta} pm2 ON pm2.post_id = p.ID AND pm2.meta_key = '_customer_user'
+                WHERE pm.meta_key = '_billing_email'
+                AND p.post_type = 'shop_order'
+                AND (pm2.meta_value = '0' OR pm2.meta_value IS NULL)"
+            );
+        }
+
+        $gauge->set( (int) $guest_orders, array( 'guest' ) );
+    }
+
     /**
      * Collect runtime metrics from stored data.
      *

src/Metrics/CustomMetricBuilder.php

@@ -0,0 +1,519 @@
+<?php
+/**
+ * Custom metric builder class.
+ *
+ * @package WP_Prometheus
+ */
+
+namespace Magdev\WpPrometheus\Metrics;
+
+// Prevent direct file access.
+if ( ! defined( 'ABSPATH' ) ) {
+	exit;
+}
+
+/**
+ * CustomMetricBuilder class.
+ *
+ * Manages custom user-defined Prometheus metrics.
+ */
+class CustomMetricBuilder {
+
+	/**
+	 * Option name for storing custom metrics.
+	 *
+	 * @var string
+	 */
+	const OPTION_NAME = 'wp_prometheus_custom_metrics';
+
+	/**
+	 * Export format version.
+	 *
+	 * @var string
+	 */
+	const EXPORT_VERSION = '1.0.0';
+
+	/**
+	 * Maximum number of labels per metric.
+	 *
+	 * @var int
+	 */
+	const MAX_LABELS = 5;
+
+	/**
+	 * Maximum number of label value combinations per metric.
+	 *
+	 * @var int
+	 */
+	const MAX_LABEL_VALUES = 50;
+
+	/**
+	 * Maximum import JSON size in bytes (1 MB).
+	 *
+	 * @var int
+	 */
+	const MAX_IMPORT_SIZE = 1048576;
+
+	/**
+	 * Get all custom metrics.
+	 *
+	 * @return array
+	 */
+	public function get_all(): array {
+		$metrics = get_option( self::OPTION_NAME, array() );
+		return is_array( $metrics ) ? $metrics : array();
+	}
+
+	/**
+	 * Get a single metric by ID.
+	 *
+	 * @param string $id Metric ID.
+	 * @return array|null
+	 */
+	public function get( string $id ): ?array {
+		$metrics = $this->get_all();
+		return $metrics[ $id ] ?? null;
+	}
+
+	/**
+	 * Save a metric (create or update).
+	 *
+	 * @param array $metric Metric data.
+	 * @return string Metric ID.
+	 * @throws \InvalidArgumentException If validation fails.
+	 */
+	public function save( array $metric ): string {
+		$errors = $this->validate( $metric );
+		if ( ! empty( $errors ) ) {
+			throw new \InvalidArgumentException( implode( ', ', $errors ) );
+		}
+
+		$metrics = $this->get_all();
+
+		// Generate ID if not provided.
+		if ( empty( $metric['id'] ) ) {
+			$metric['id'] = wp_generate_uuid4();
+			$metric['created_at'] = time();
+		}
+
+		$metric['updated_at'] = time();
+
+		// Sanitize and normalize the metric data.
+		$metric = $this->sanitize_metric( $metric );
+
+		$metrics[ $metric['id'] ] = $metric;
+		update_option( self::OPTION_NAME, $metrics );
+
+		return $metric['id'];
+	}
+
+	/**
+	 * Delete a metric.
+	 *
+	 * @param string $id Metric ID.
+	 * @return bool True if deleted, false if not found.
+	 */
+	public function delete( string $id ): bool {
+		$metrics = $this->get_all();
+
+		if ( ! isset( $metrics[ $id ] ) ) {
+			return false;
+		}
+
+		unset( $metrics[ $id ] );
+		update_option( self::OPTION_NAME, $metrics );
+
+		return true;
+	}
+
+	/**
+	 * Validate a Prometheus metric name.
+	 *
+	 * @param string $name Metric name.
+	 * @return bool True if valid.
+	 */
+	public function validate_name( string $name ): bool {
+		// Prometheus metric names must match: [a-zA-Z_:][a-zA-Z0-9_:]*
+		return (bool) preg_match( '/^[a-zA-Z_:][a-zA-Z0-9_:]*$/', $name );
+	}
+
+	/**
+	 * Validate a Prometheus label name.
+	 *
+	 * @param string $name Label name.
+	 * @return bool True if valid.
+	 */
+	public function validate_label_name( string $name ): bool {
+		// Prometheus label names must match: [a-zA-Z_][a-zA-Z0-9_]*
+		// Labels starting with __ are reserved.
+		if ( strpos( $name, '__' ) === 0 ) {
+			return false;
+		}
+		return (bool) preg_match( '/^[a-zA-Z_][a-zA-Z0-9_]*$/', $name );
+	}
+
+	/**
+	 * Validate a complete metric definition.
+	 *
+	 * @param array $metric Metric data.
+	 * @return array Array of error messages (empty if valid).
+	 */
+	public function validate( array $metric ): array {
+		$errors = array();
+
+		// Name is required.
+		if ( empty( $metric['name'] ) ) {
+			$errors[] = __( 'Metric name is required.', 'wp-prometheus' );
+		} elseif ( ! $this->validate_name( $metric['name'] ) ) {
+			$errors[] = __( 'Metric name must start with a letter, underscore, or colon, and contain only letters, numbers, underscores, and colons.', 'wp-prometheus' );
+		}
+
+		// Check for reserved prefixes.
+		if ( ! empty( $metric['name'] ) ) {
+			$reserved_prefixes = array( 'wordpress_', 'go_', 'process_', 'promhttp_' );
+			foreach ( $reserved_prefixes as $prefix ) {
+				if ( strpos( $metric['name'], $prefix ) === 0 ) {
+					$errors[] = sprintf(
+						/* translators: %s: Reserved prefix */
+						__( 'Metric name cannot start with reserved prefix "%s".', 'wp-prometheus' ),
+						$prefix
+					);
+					break;
+				}
+			}
+		}
+
+		// Check for duplicate names (excluding current metric if editing).
+		if ( ! empty( $metric['name'] ) ) {
+			$existing = $this->get_all();
+			foreach ( $existing as $id => $existing_metric ) {
+				if ( $existing_metric['name'] === $metric['name'] && ( empty( $metric['id'] ) || $metric['id'] !== $id ) ) {
+					$errors[] = __( 'A metric with this name already exists.', 'wp-prometheus' );
+					break;
+				}
+			}
+		}
+
+		// Help text is required.
+		if ( empty( $metric['help'] ) ) {
+			$errors[] = __( 'Help text is required.', 'wp-prometheus' );
+		}
+
+		// Validate type.
+		$valid_types = array( 'gauge' );
+		if ( empty( $metric['type'] ) || ! in_array( $metric['type'], $valid_types, true ) ) {
+			$errors[] = __( 'Invalid metric type. Only gauge is supported.', 'wp-prometheus' );
+		}
+
+		// Validate labels.
+		if ( ! empty( $metric['labels'] ) ) {
+			if ( ! is_array( $metric['labels'] ) ) {
+				$errors[] = __( 'Labels must be an array.', 'wp-prometheus' );
+			} elseif ( count( $metric['labels'] ) > self::MAX_LABELS ) {
+				$errors[] = sprintf(
+					/* translators: %d: Maximum labels */
+					__( 'Maximum %d labels allowed per metric.', 'wp-prometheus' ),
+					self::MAX_LABELS
+				);
+			} else {
+				foreach ( $metric['labels'] as $label ) {
+					if ( ! $this->validate_label_name( $label ) ) {
+						$errors[] = sprintf(
+							/* translators: %s: Label name */
+							__( 'Invalid label name: %s', 'wp-prometheus' ),
+							$label
+						);
+					}
+				}
+			}
+		}
+
+		// Validate value type.
+		$valid_value_types = array( 'static', 'option' );
+		if ( empty( $metric['value_type'] ) || ! in_array( $metric['value_type'], $valid_value_types, true ) ) {
+			$errors[] = __( 'Invalid value type. Must be "static" or "option".', 'wp-prometheus' );
+		}
+
+		// Validate value config based on type.
+		if ( ! empty( $metric['value_type'] ) ) {
+			if ( 'static' === $metric['value_type'] ) {
+				// Static values validated in label_values.
+			} elseif ( 'option' === $metric['value_type'] ) {
+				if ( empty( $metric['value_config']['option_name'] ) ) {
+					$errors[] = __( 'Option name is required for option-based metrics.', 'wp-prometheus' );
+				}
+			}
+		}
+
+		// Validate label values count.
+		if ( ! empty( $metric['label_values'] ) && is_array( $metric['label_values'] ) ) {
+			if ( count( $metric['label_values'] ) > self::MAX_LABEL_VALUES ) {
+				$errors[] = sprintf(
+					/* translators: %d: Maximum label combinations */
+					__( 'Maximum %d label value combinations allowed.', 'wp-prometheus' ),
+					self::MAX_LABEL_VALUES
+				);
+			}
+
+			// Validate each row has correct number of values.
+			$label_count = count( $metric['labels'] ?? array() );
+			foreach ( $metric['label_values'] as $row ) {
+				if ( is_array( $row ) && count( $row ) !== $label_count + 1 ) { // +1 for value.
+					$errors[] = __( 'Each label value row must have values for all labels plus a metric value.', 'wp-prometheus' );
+					break;
+				}
+			}
+		}
+
+		return $errors;
+	}
+
+	/**
+	 * Sanitize metric data.
+	 *
+	 * @param array $metric Raw metric data.
+	 * @return array Sanitized metric data.
+	 */
+	private function sanitize_metric( array $metric ): array {
+		$sanitized = array(
+			'id'           => sanitize_key( $metric['id'] ?? '' ),
+			'name'         => sanitize_key( $metric['name'] ?? '' ),
+			'help'         => sanitize_text_field( $metric['help'] ?? '' ),
+			'type'         => sanitize_key( $metric['type'] ?? 'gauge' ),
+			'labels'       => array(),
+			'value_type'   => sanitize_key( $metric['value_type'] ?? 'static' ),
+			'value_config' => array(),
+			'label_values' => array(),
+			'enabled'      => ! empty( $metric['enabled'] ),
+			'created_at'   => absint( $metric['created_at'] ?? time() ),
+			'updated_at'   => absint( $metric['updated_at'] ?? time() ),
+		);
+
+		// Sanitize labels.
+		if ( ! empty( $metric['labels'] ) && is_array( $metric['labels'] ) ) {
+			foreach ( $metric['labels'] as $label ) {
+				$sanitized['labels'][] = sanitize_key( $label );
+			}
+		}
+
+		// Sanitize value config.
+		if ( 'static' === $sanitized['value_type'] ) {
+			$sanitized['value_config'] = array();
+		} elseif ( 'option' === $sanitized['value_type'] ) {
+			$sanitized['value_config'] = array(
+				'option_name' => sanitize_key( $metric['value_config']['option_name'] ?? '' ),
+				'default'     => floatval( $metric['value_config']['default'] ?? 0 ),
+			);
+		}
+
+		// Sanitize label values.
+		if ( ! empty( $metric['label_values'] ) && is_array( $metric['label_values'] ) ) {
+			foreach ( $metric['label_values'] as $row ) {
+				if ( is_array( $row ) ) {
+					$sanitized_row = array();
+					foreach ( $row as $index => $value ) {
+						// Last value is the metric value (numeric).
+						if ( $index === count( $row ) - 1 ) {
+							$sanitized_row[] = floatval( $value );
+						} else {
+							$sanitized_row[] = sanitize_text_field( $value );
+						}
+					}
+					$sanitized['label_values'][] = $sanitized_row;
+				}
+			}
+		}
+
+		return $sanitized;
+	}
+
+	/**
+	 * Export all metrics to JSON.
+	 *
+	 * @return string JSON string.
+	 */
+	public function export(): string {
+		$metrics = $this->get_all();
+
+		$export_data = array(
+			'version'        => self::EXPORT_VERSION,
+			'plugin_version' => WP_PROMETHEUS_VERSION,
+			'exported_at'    => gmdate( 'c' ),
+			'metrics'        => array_values( $metrics ),
+		);
+
+		return wp_json_encode( $export_data, JSON_PRETTY_PRINT );
+	}
+
+	/**
+	 * Import metrics from JSON.
+	 *
+	 * @param string $json      JSON string.
+	 * @param string $mode      Import mode: 'skip', 'overwrite', or 'rename'.
+	 * @return array Result with 'imported', 'skipped', 'errors' counts.
+	 * @throws \InvalidArgumentException If JSON is invalid.
+	 */
+	public function import( string $json, string $mode = 'skip' ): array {
+		// Prevent DoS via excessively large imports.
+		if ( strlen( $json ) > self::MAX_IMPORT_SIZE ) {
+			throw new \InvalidArgumentException(
+				sprintf(
+					/* translators: %s: Maximum size */
+					__( 'Import data exceeds maximum size of %s.', 'wp-prometheus' ),
+					size_format( self::MAX_IMPORT_SIZE )
+				)
+			);
+		}
+
+		$data = json_decode( $json, true );
+
+		if ( json_last_error() !== JSON_ERROR_NONE ) {
+			throw new \InvalidArgumentException( __( 'Invalid JSON format.', 'wp-prometheus' ) );
+		}
+
+		if ( empty( $data['metrics'] ) || ! is_array( $data['metrics'] ) ) {
+			throw new \InvalidArgumentException( __( 'No metrics found in import file.', 'wp-prometheus' ) );
+		}
+
+		// Validate import mode.
+		$valid_modes = array( 'skip', 'overwrite', 'rename' );
+		if ( ! in_array( $mode, $valid_modes, true ) ) {
+			$mode = 'skip';
+		}
+
+		$result = array(
+			'imported' => 0,
+			'skipped'  => 0,
+			'errors'   => 0,
+			'messages' => array(),
+		);
+
+		$existing_metrics = $this->get_all();
+		$existing_names   = array_column( $existing_metrics, 'name', 'id' );
+
+		foreach ( $data['metrics'] as $metric ) {
+			if ( empty( $metric['name'] ) ) {
+				$result['errors']++;
+				continue;
+			}
+
+			// Check for name collision.
+			$name_exists = in_array( $metric['name'], $existing_names, true );
+
+			if ( $name_exists ) {
+				if ( 'skip' === $mode ) {
+					$result['skipped']++;
+					$result['messages'][] = sprintf(
+						/* translators: %s: Metric name */
+						__( 'Skipped "%s" (already exists).', 'wp-prometheus' ),
+						$metric['name']
+					);
+					continue;
+				} elseif ( 'rename' === $mode ) {
+					// Generate unique name.
+					$base_name = $metric['name'];
+					$counter   = 1;
+					while ( in_array( $metric['name'], $existing_names, true ) ) {
+						$metric['name'] = $base_name . '_imported_' . $counter;
+						$counter++;
+					}
+				}
+				// 'overwrite' mode: continue with same name, will overwrite below.
+			}
+
+			// Clear ID to create new metric (unless overwriting).
+			if ( 'overwrite' === $mode && $name_exists ) {
+				// Find existing ID by name.
+				$metric['id'] = array_search( $metric['name'], $existing_names, true );
+			} else {
+				unset( $metric['id'] );
+			}
+
+			try {
+				$this->save( $metric );
+				$result['imported']++;
+
+				// Update existing names for subsequent collision checks.
+				$existing_names = array_column( $this->get_all(), 'name', 'id' );
+			} catch ( \InvalidArgumentException $e ) {
+				$result['errors']++;
+				$result['messages'][] = sprintf(
+					/* translators: 1: Metric name, 2: Error message */
+					__( 'Error importing "%1$s": %2$s', 'wp-prometheus' ),
+					$metric['name'],
+					$e->getMessage()
+				);
+			}
+		}
+
+		return $result;
+	}
+
+	/**
+	 * Register custom metrics with the Collector.
+	 *
+	 * @param Collector $collector The metrics collector instance.
+	 * @return void
+	 */
+	public function register_with_collector( Collector $collector ): void {
+		$metrics = $this->get_all();
+
+		foreach ( $metrics as $metric ) {
+			if ( empty( $metric['enabled'] ) ) {
+				continue;
+			}
+
+			try {
+				$gauge = $collector->register_gauge(
+					$metric['name'],
+					$metric['help'],
+					$metric['labels'] ?? array()
+				);
+
+				// Set values based on value type.
+				if ( 'option' === $metric['value_type'] ) {
+					// Option-based metric: read from WordPress option.
+					$option_name = $metric['value_config']['option_name'] ?? '';
+					$default     = $metric['value_config']['default'] ?? 0;
+
+					if ( ! empty( $option_name ) ) {
+						$value = get_option( $option_name, $default );
+						$value = is_numeric( $value ) ? floatval( $value ) : $default;
+
+						// For option-based, use empty labels if no labels defined.
+						$label_values = array();
+						if ( ! empty( $metric['labels'] ) && ! empty( $metric['label_values'][0] ) ) {
+							// Use first row of labels (without the value).
+							$label_values = array_slice( $metric['label_values'][0], 0, count( $metric['labels'] ) );
+						}
+
+						$gauge->set( $value, $label_values );
+					}
+				} elseif ( 'static' === $metric['value_type'] ) {
+					// Static metric: use predefined label values.
+					if ( ! empty( $metric['label_values'] ) ) {
+						foreach ( $metric['label_values'] as $row ) {
+							if ( ! is_array( $row ) || count( $row ) < 1 ) {
+								continue;
+							}
+
+							// Last element is the value.
+							$value = array_pop( $row );
+
+							// Remaining elements are label values.
+							$gauge->set( floatval( $value ), $row );
+						}
+					} else {
+						// No labels, single value.
+						$gauge->set( 0, array() );
+					}
+				}
+			} catch ( \Exception $e ) {
+				// Log error but don't break metric collection.
+				if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+					error_log( sprintf( 'WP Prometheus: Failed to register custom metric "%s": %s', $metric['name'], $e->getMessage() ) );
+				}
+			}
+		}
+	}
+}

src/Metrics/StorageFactory.php

@@ -0,0 +1,502 @@
+<?php
+/**
+ * Storage factory for Prometheus metrics.
+ *
+ * @package WP_Prometheus
+ */
+
+namespace Magdev\WpPrometheus\Metrics;
+
+use Prometheus\Storage\Adapter;
+use Prometheus\Storage\InMemory;
+use Prometheus\Storage\Redis;
+use Prometheus\Storage\APC;
+use Prometheus\Exception\StorageException;
+
+// Prevent direct file access.
+if ( ! defined( 'ABSPATH' ) ) {
+	exit;
+}
+
+/**
+ * StorageFactory class.
+ *
+ * Creates and configures storage adapters for Prometheus metrics.
+ * Supports configuration via WordPress options or environment variables.
+ */
+class StorageFactory {
+
+	/**
+	 * Available storage adapters.
+	 */
+	public const ADAPTER_INMEMORY = 'inmemory';
+	public const ADAPTER_REDIS    = 'redis';
+	public const ADAPTER_APCU     = 'apcu';
+
+	/**
+	 * Environment variable names.
+	 */
+	private const ENV_STORAGE_ADAPTER  = 'WP_PROMETHEUS_STORAGE_ADAPTER';
+	private const ENV_REDIS_HOST       = 'WP_PROMETHEUS_REDIS_HOST';
+	private const ENV_REDIS_PORT       = 'WP_PROMETHEUS_REDIS_PORT';
+	private const ENV_REDIS_PASSWORD   = 'WP_PROMETHEUS_REDIS_PASSWORD';
+	private const ENV_REDIS_DATABASE   = 'WP_PROMETHEUS_REDIS_DATABASE';
+	private const ENV_REDIS_PREFIX     = 'WP_PROMETHEUS_REDIS_PREFIX';
+	private const ENV_APCU_PREFIX      = 'WP_PROMETHEUS_APCU_PREFIX';
+
+	/**
+	 * Default Redis prefix.
+	 */
+	private const DEFAULT_REDIS_PREFIX = 'WORDPRESS_PROMETHEUS_';
+
+	/**
+	 * Default APCu prefix.
+	 */
+	private const DEFAULT_APCU_PREFIX = 'wp_prom';
+
+	/**
+	 * Singleton instance of the storage adapter.
+	 *
+	 * @var Adapter|null
+	 */
+	private static ?Adapter $instance = null;
+
+	/**
+	 * Last error message.
+	 *
+	 * @var string
+	 */
+	private static string $last_error = '';
+
+	/**
+	 * Get the storage adapter instance.
+	 *
+	 * @return Adapter
+	 */
+	public static function get_adapter(): Adapter {
+		if ( null === self::$instance ) {
+			self::$instance = self::create_adapter();
+		}
+		return self::$instance;
+	}
+
+	/**
+	 * Reset the singleton instance (useful for testing or config changes).
+	 *
+	 * @return void
+	 */
+	public static function reset(): void {
+		self::$instance = null;
+		self::$last_error = '';
+	}
+
+	/**
+	 * Get the last error message.
+	 *
+	 * @return string
+	 */
+	public static function get_last_error(): string {
+		return self::$last_error;
+	}
+
+	/**
+	 * Get available storage adapters.
+	 *
+	 * @return array<string, string>
+	 */
+	public static function get_available_adapters(): array {
+		return array(
+			self::ADAPTER_INMEMORY => __( 'In-Memory (default, no persistence)', 'wp-prometheus' ),
+			self::ADAPTER_REDIS    => __( 'Redis (requires PHP Redis extension)', 'wp-prometheus' ),
+			self::ADAPTER_APCU     => __( 'APCu (requires APCu extension)', 'wp-prometheus' ),
+		);
+	}
+
+	/**
+	 * Check if a storage adapter is available on this system.
+	 *
+	 * @param string $adapter Adapter name.
+	 * @return bool
+	 */
+	public static function is_adapter_available( string $adapter ): bool {
+		switch ( $adapter ) {
+			case self::ADAPTER_INMEMORY:
+				return true;
+
+			case self::ADAPTER_REDIS:
+				return extension_loaded( 'redis' );
+
+			case self::ADAPTER_APCU:
+				return extension_loaded( 'apcu' ) && apcu_enabled();
+
+			default:
+				return false;
+		}
+	}
+
+	/**
+	 * Get the configured storage adapter name.
+	 *
+	 * @return string
+	 */
+	public static function get_configured_adapter(): string {
+		// Check environment variable first.
+		$env_adapter = getenv( self::ENV_STORAGE_ADAPTER );
+		if ( false !== $env_adapter && ! empty( $env_adapter ) ) {
+			return strtolower( $env_adapter );
+		}
+
+		// Fall back to WordPress option.
+		return get_option( 'wp_prometheus_storage_adapter', self::ADAPTER_INMEMORY );
+	}
+
+	/**
+	 * Get the active storage adapter name (may differ from configured if fallback occurred).
+	 *
+	 * @return string
+	 */
+	public static function get_active_adapter(): string {
+		// Ensure adapter is created.
+		self::get_adapter();
+
+		$configured = self::get_configured_adapter();
+		if ( self::is_adapter_available( $configured ) && empty( self::$last_error ) ) {
+			return $configured;
+		}
+
+		return self::ADAPTER_INMEMORY;
+	}
+
+	/**
+	 * Create the storage adapter based on configuration.
+	 *
+	 * @return Adapter
+	 */
+	private static function create_adapter(): Adapter {
+		$adapter = self::get_configured_adapter();
+		self::$last_error = '';
+
+		switch ( $adapter ) {
+			case self::ADAPTER_REDIS:
+				return self::create_redis_adapter();
+
+			case self::ADAPTER_APCU:
+				return self::create_apcu_adapter();
+
+			case self::ADAPTER_INMEMORY:
+			default:
+				return new InMemory();
+		}
+	}
+
+	/**
+	 * Create Redis storage adapter.
+	 *
+	 * @return Adapter
+	 */
+	private static function create_redis_adapter(): Adapter {
+		if ( ! extension_loaded( 'redis' ) ) {
+			self::$last_error = __( 'PHP Redis extension is not installed.', 'wp-prometheus' );
+			return new InMemory();
+		}
+
+		$config = self::get_redis_config();
+
+		try {
+			Redis::setPrefix( $config['prefix'] );
+
+			$redis = new Redis( array(
+				'host'                   => $config['host'],
+				'port'                   => $config['port'],
+				'password'               => $config['password'] ?: null,
+				'timeout'                => 0.5,
+				'read_timeout'           => 10,
+				'persistent_connections' => true,
+			) );
+
+			// Test connection by triggering initialization.
+			// The Redis adapter connects lazily, so we need to check it works.
+			return $redis;
+		} catch ( StorageException $e ) {
+			self::$last_error = sprintf(
+				/* translators: %s: Error message */
+				__( 'Redis connection failed: %s', 'wp-prometheus' ),
+				$e->getMessage()
+			);
+			return new InMemory();
+		} catch ( \RedisException $e ) {
+			self::$last_error = sprintf(
+				/* translators: %s: Error message */
+				__( 'Redis error: %s', 'wp-prometheus' ),
+				$e->getMessage()
+			);
+			return new InMemory();
+		} catch ( \Exception $e ) {
+			self::$last_error = sprintf(
+				/* translators: %s: Error message */
+				__( 'Storage error: %s', 'wp-prometheus' ),
+				$e->getMessage()
+			);
+			return new InMemory();
+		}
+	}
+
+	/**
+	 * Create APCu storage adapter.
+	 *
+	 * @return Adapter
+	 */
+	private static function create_apcu_adapter(): Adapter {
+		if ( ! extension_loaded( 'apcu' ) ) {
+			self::$last_error = __( 'APCu extension is not installed.', 'wp-prometheus' );
+			return new InMemory();
+		}
+
+		if ( ! apcu_enabled() ) {
+			self::$last_error = __( 'APCu is installed but not enabled.', 'wp-prometheus' );
+			return new InMemory();
+		}
+
+		$prefix = self::get_apcu_prefix();
+
+		try {
+			return new APC( $prefix );
+		} catch ( StorageException $e ) {
+			self::$last_error = sprintf(
+				/* translators: %s: Error message */
+				__( 'APCu error: %s', 'wp-prometheus' ),
+				$e->getMessage()
+			);
+			return new InMemory();
+		}
+	}
+
+	/**
+	 * Get Redis configuration.
+	 *
+	 * @return array{host: string, port: int, password: string, database: int, prefix: string}
+	 */
+	public static function get_redis_config(): array {
+		// Check environment variables first.
+		$env_host = getenv( self::ENV_REDIS_HOST );
+		$env_port = getenv( self::ENV_REDIS_PORT );
+		$env_password = getenv( self::ENV_REDIS_PASSWORD );
+		$env_database = getenv( self::ENV_REDIS_DATABASE );
+		$env_prefix = getenv( self::ENV_REDIS_PREFIX );
+
+		// Get WordPress options as fallback.
+		$options = get_option( 'wp_prometheus_redis_config', array() );
+
+		return array(
+			'host'     => ( false !== $env_host && ! empty( $env_host ) ) ? $env_host : ( $options['host'] ?? '127.0.0.1' ),
+			'port'     => ( false !== $env_port && ! empty( $env_port ) ) ? (int) $env_port : ( (int) ( $options['port'] ?? 6379 ) ),
+			'password' => ( false !== $env_password ) ? $env_password : ( $options['password'] ?? '' ),
+			'database' => ( false !== $env_database && ! empty( $env_database ) ) ? (int) $env_database : ( (int) ( $options['database'] ?? 0 ) ),
+			'prefix'   => ( false !== $env_prefix && ! empty( $env_prefix ) ) ? $env_prefix : ( $options['prefix'] ?? self::DEFAULT_REDIS_PREFIX ),
+		);
+	}
+
+	/**
+	 * Get APCu prefix.
+	 *
+	 * @return string
+	 */
+	public static function get_apcu_prefix(): string {
+		$env_prefix = getenv( self::ENV_APCU_PREFIX );
+		if ( false !== $env_prefix && ! empty( $env_prefix ) ) {
+			return $env_prefix;
+		}
+
+		return get_option( 'wp_prometheus_apcu_prefix', self::DEFAULT_APCU_PREFIX );
+	}
+
+	/**
+	 * Save storage configuration.
+	 *
+	 * @param array $config Configuration array.
+	 * @return void
+	 */
+	public static function save_config( array $config ): void {
+		if ( isset( $config['adapter'] ) ) {
+			update_option( 'wp_prometheus_storage_adapter', sanitize_key( $config['adapter'] ) );
+		}
+
+		if ( isset( $config['redis'] ) && is_array( $config['redis'] ) ) {
+			$redis_config = array(
+				'host'     => sanitize_text_field( $config['redis']['host'] ?? '127.0.0.1' ),
+				'port'     => absint( $config['redis']['port'] ?? 6379 ),
+				'password' => sanitize_text_field( $config['redis']['password'] ?? '' ),
+				'database' => absint( $config['redis']['database'] ?? 0 ),
+				'prefix'   => sanitize_key( $config['redis']['prefix'] ?? self::DEFAULT_REDIS_PREFIX ),
+			);
+			update_option( 'wp_prometheus_redis_config', $redis_config );
+		}
+
+		if ( isset( $config['apcu_prefix'] ) ) {
+			update_option( 'wp_prometheus_apcu_prefix', sanitize_key( $config['apcu_prefix'] ) );
+		}
+
+		// Reset the singleton to apply new configuration.
+		self::reset();
+	}
+
+	/**
+	 * Test storage adapter connection.
+	 *
+	 * @param string $adapter Adapter name.
+	 * @param array  $config  Optional configuration to test.
+	 * @return array{success: bool, message: string}
+	 */
+	public static function test_connection( string $adapter, array $config = array() ): array {
+		switch ( $adapter ) {
+			case self::ADAPTER_REDIS:
+				return self::test_redis_connection( $config );
+
+			case self::ADAPTER_APCU:
+				return self::test_apcu_connection( $config );
+
+			case self::ADAPTER_INMEMORY:
+				return array(
+					'success' => true,
+					'message' => __( 'In-Memory storage is always available.', 'wp-prometheus' ),
+				);
+
+			default:
+				return array(
+					'success' => false,
+					'message' => __( 'Unknown storage adapter.', 'wp-prometheus' ),
+				);
+		}
+	}
+
+	/**
+	 * Test Redis connection.
+	 *
+	 * @param array $config Redis configuration.
+	 * @return array{success: bool, message: string}
+	 */
+	private static function test_redis_connection( array $config ): array {
+		if ( ! extension_loaded( 'redis' ) ) {
+			return array(
+				'success' => false,
+				'message' => __( 'PHP Redis extension is not installed.', 'wp-prometheus' ),
+			);
+		}
+
+		$redis_config = ! empty( $config ) ? $config : self::get_redis_config();
+
+		try {
+			$redis = new \Redis();
+
+			$connected = $redis->connect(
+				$redis_config['host'],
+				$redis_config['port'],
+				0.5 // timeout
+			);
+
+			if ( ! $connected ) {
+				return array(
+					'success' => false,
+					'message' => __( 'Could not connect to Redis server.', 'wp-prometheus' ),
+				);
+			}
+
+			if ( ! empty( $redis_config['password'] ) ) {
+				$authenticated = $redis->auth( $redis_config['password'] );
+				if ( ! $authenticated ) {
+					return array(
+						'success' => false,
+						'message' => __( 'Redis authentication failed.', 'wp-prometheus' ),
+					);
+				}
+			}
+
+			if ( $redis_config['database'] > 0 ) {
+				$redis->select( $redis_config['database'] );
+			}
+
+			// Test with a ping.
+			$pong = $redis->ping();
+			$redis->close();
+
+			if ( $pong ) {
+				return array(
+					'success' => true,
+					'message' => sprintf(
+						/* translators: %s: Redis host:port */
+						__( 'Successfully connected to Redis at %s.', 'wp-prometheus' ),
+						$redis_config['host'] . ':' . $redis_config['port']
+					),
+				);
+			}
+
+			return array(
+				'success' => false,
+				'message' => __( 'Redis ping failed.', 'wp-prometheus' ),
+			);
+		} catch ( \RedisException $e ) {
+			return array(
+				'success' => false,
+				'message' => sprintf(
+					/* translators: %s: Error message */
+					__( 'Redis error: %s', 'wp-prometheus' ),
+					$e->getMessage()
+				),
+			);
+		}
+	}
+
+	/**
+	 * Test APCu connection.
+	 *
+	 * @param array $config APCu configuration.
+	 * @return array{success: bool, message: string}
+	 */
+	private static function test_apcu_connection( array $config ): array {
+		if ( ! extension_loaded( 'apcu' ) ) {
+			return array(
+				'success' => false,
+				'message' => __( 'APCu extension is not installed.', 'wp-prometheus' ),
+			);
+		}
+
+		if ( ! apcu_enabled() ) {
+			return array(
+				'success' => false,
+				'message' => __( 'APCu is installed but not enabled. Check your php.ini settings.', 'wp-prometheus' ),
+			);
+		}
+
+		// Test with a simple store/fetch.
+		$test_key = 'wp_prometheus_test_' . time();
+		$test_value = 'test_' . wp_rand();
+
+		$stored = apcu_store( $test_key, $test_value, 5 );
+		if ( ! $stored ) {
+			return array(
+				'success' => false,
+				'message' => __( 'APCu store operation failed.', 'wp-prometheus' ),
+			);
+		}
+
+		$fetched = apcu_fetch( $test_key );
+		apcu_delete( $test_key );
+
+		if ( $fetched === $test_value ) {
+			$info = apcu_cache_info( true );
+			return array(
+				'success' => true,
+				'message' => sprintf(
+					/* translators: %s: Memory info */
+					__( 'APCu is working. Memory: %s used.', 'wp-prometheus' ),
+					size_format( $info['mem_size'] ?? 0 )
+				),
+			);
+		}
+
+		return array(
+			'success' => false,
+			'message' => __( 'APCu fetch operation returned unexpected value.', 'wp-prometheus' ),
+		);
+	}
+}

src/Plugin.php

@@ -57,7 +57,9 @@ final class Plugin {
     private function __construct() {
         $this->init_components();
         $this->init_hooks();
-        $this->load_textdomain();
+
+        // Defer textdomain loading to 'init' action (required since WordPress 6.7).
+        add_action( 'init', array( $this, 'load_textdomain' ) );
     }
 
     /**
@@ -144,9 +146,11 @@ final class Plugin {
     /**
      * Load plugin textdomain.
      *
+     * Hooked to 'init' action to comply with WordPress 6.7+ requirements.
+     *
      * @return void
      */
-    private function load_textdomain(): void {
+    public function load_textdomain(): void {
         load_plugin_textdomain(
             'wp-prometheus',
             false,

tests/Helpers/GlobalFunctionState.php

@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Magdev\WpPrometheus\Tests\Helpers;
+
+/**
+ * Controllable state for global WordPress function stubs.
+ *
+ * Used by the bootstrap's global get_option() stub so that tests
+ * for global-scope functions (e.g., wp_prometheus_authenticate_request)
+ * can control return values without php-mock (which requires namespaces).
+ */
+class GlobalFunctionState
+{
+    /** @var array<string, mixed> Simulated WordPress options. */
+    public static array $options = [];
+
+    /** @var array<string, int> Track function call counts. */
+    public static array $callCounts = [];
+
+    /** @var array<string, list<mixed>> Track arguments passed to functions. */
+    public static array $callArgs = [];
+
+    /**
+     * Reset all state. Call in setUp()/tearDown().
+     */
+    public static function reset(): void
+    {
+        self::$options = [];
+        self::$callCounts = [];
+        self::$callArgs = [];
+    }
+
+    /**
+     * Record a function call for later assertions.
+     */
+    public static function recordCall(string $function, mixed ...$args): void
+    {
+        self::$callCounts[$function] = (self::$callCounts[$function] ?? 0) + 1;
+        self::$callArgs[$function][] = $args;
+    }
+
+    /**
+     * Get call count for a function.
+     */
+    public static function getCallCount(string $function): int
+    {
+        return self::$callCounts[$function] ?? 0;
+    }
+}

tests/Unit/Admin/DashboardProviderTest.php

@@ -0,0 +1,376 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Magdev\WpPrometheus\Tests\Unit\Admin;
+
+use Magdev\WpPrometheus\Admin\DashboardProvider;
+use Magdev\WpPrometheus\Tests\Helpers\GlobalFunctionState;
+use Magdev\WpPrometheus\Tests\Unit\TestCase;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\Test;
+
+#[CoversClass(DashboardProvider::class)]
+class DashboardProviderTest extends TestCase
+{
+    private DashboardProvider $provider;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->provider = new DashboardProvider();
+    }
+
+    // ── register_dashboard() - Validation ────────────────────────────
+
+    #[Test]
+    public function register_with_inline_json_succeeds(): void
+    {
+        $result = $this->provider->register_dashboard('my-dashboard', [
+            'title' => 'My Dashboard',
+            'json'  => '{"panels":[]}',
+        ]);
+
+        $this->assertTrue($result);
+    }
+
+    #[Test]
+    public function register_rejects_empty_slug(): void
+    {
+        $result = $this->provider->register_dashboard('', [
+            'title' => 'Test',
+            'json'  => '{}',
+        ]);
+
+        $this->assertFalse($result);
+    }
+
+    #[Test]
+    public function register_rejects_invalid_slug_characters(): void
+    {
+        // sanitize_key removes all non [a-z0-9_-] characters
+        // A slug like '!@#' becomes '' after sanitize_key
+        $result = $this->provider->register_dashboard('!@#', [
+            'title' => 'Test',
+            'json'  => '{}',
+        ]);
+
+        $this->assertFalse($result);
+    }
+
+    #[Test]
+    public function register_rejects_duplicate_builtin_slug(): void
+    {
+        $result = $this->provider->register_dashboard('wordpress-overview', [
+            'title' => 'Override Built-in',
+            'json'  => '{}',
+        ]);
+
+        $this->assertFalse($result);
+    }
+
+    #[Test]
+    public function register_rejects_duplicate_registered_slug(): void
+    {
+        $this->provider->register_dashboard('my-dashboard', [
+            'title' => 'First',
+            'json'  => '{}',
+        ]);
+
+        $result = $this->provider->register_dashboard('my-dashboard', [
+            'title' => 'Second',
+            'json'  => '{}',
+        ]);
+
+        $this->assertFalse($result);
+    }
+
+    #[Test]
+    public function register_requires_title(): void
+    {
+        $result = $this->provider->register_dashboard('no-title', [
+            'json' => '{}',
+        ]);
+
+        $this->assertFalse($result);
+    }
+
+    #[Test]
+    public function register_requires_file_or_json(): void
+    {
+        $result = $this->provider->register_dashboard('no-content', [
+            'title' => 'No Content',
+        ]);
+
+        $this->assertFalse($result);
+    }
+
+    #[Test]
+    public function register_rejects_both_file_and_json(): void
+    {
+        $fileExists = $this->getFunctionMock('Magdev\\WpPrometheus\\Admin', 'file_exists');
+        $fileExists->expects($this->any())->willReturn(true);
+
+        $isReadable = $this->getFunctionMock('Magdev\\WpPrometheus\\Admin', 'is_readable');
+        $isReadable->expects($this->any())->willReturn(true);
+
+        $realpath = $this->getFunctionMock('Magdev\\WpPrometheus\\Admin', 'realpath');
+        $realpath->expects($this->any())->willReturnArgument(0);
+
+        $result = $this->provider->register_dashboard('both', [
+            'title' => 'Both',
+            'file'  => '/tmp/wordpress/wp-content/plugins/test/dashboard.json',
+            'json'  => '{}',
+        ]);
+
+        $this->assertFalse($result);
+    }
+
+    #[Test]
+    public function register_file_requires_absolute_path(): void
+    {
+        $result = $this->provider->register_dashboard('relative', [
+            'title' => 'Relative Path',
+            'file'  => 'relative/path/dashboard.json',
+        ]);
+
+        $this->assertFalse($result);
+    }
+
+    #[Test]
+    public function register_file_must_exist(): void
+    {
+        $fileExists = $this->getFunctionMock('Magdev\\WpPrometheus\\Admin', 'file_exists');
+        $fileExists->expects($this->any())->willReturn(false);
+
+        $result = $this->provider->register_dashboard('missing-file', [
+            'title' => 'Missing File',
+            'file'  => '/tmp/wordpress/wp-content/plugins/test/nonexistent.json',
+        ]);
+
+        $this->assertFalse($result);
+    }
+
+    #[Test]
+    public function register_file_rejects_path_traversal(): void
+    {
+        $fileExists = $this->getFunctionMock('Magdev\\WpPrometheus\\Admin', 'file_exists');
+        $fileExists->expects($this->any())->willReturn(true);
+
+        $isReadable = $this->getFunctionMock('Magdev\\WpPrometheus\\Admin', 'is_readable');
+        $isReadable->expects($this->any())->willReturn(true);
+
+        $realpath = $this->getFunctionMock('Magdev\\WpPrometheus\\Admin', 'realpath');
+        $realpath->expects($this->any())->willReturnArgument(0);
+
+        $result = $this->provider->register_dashboard('evil', [
+            'title' => 'Evil Dashboard',
+            'file'  => '/etc/passwd',
+        ]);
+
+        $this->assertFalse($result);
+    }
+
+    #[Test]
+    public function register_file_accepts_path_under_wp_content(): void
+    {
+        $fileExists = $this->getFunctionMock('Magdev\\WpPrometheus\\Admin', 'file_exists');
+        $fileExists->expects($this->any())->willReturn(true);
+
+        $isReadable = $this->getFunctionMock('Magdev\\WpPrometheus\\Admin', 'is_readable');
+        $isReadable->expects($this->any())->willReturn(true);
+
+        $realpath = $this->getFunctionMock('Magdev\\WpPrometheus\\Admin', 'realpath');
+        $realpath->expects($this->any())->willReturnArgument(0);
+
+        $result = $this->provider->register_dashboard('valid-file', [
+            'title' => 'Valid File Dashboard',
+            'file'  => '/tmp/wordpress/wp-content/plugins/my-plugin/dashboard.json',
+        ]);
+
+        $this->assertTrue($result);
+    }
+
+    #[Test]
+    public function register_rejects_invalid_inline_json(): void
+    {
+        $result = $this->provider->register_dashboard('bad-json', [
+            'title' => 'Bad JSON',
+            'json'  => '{invalid json',
+        ]);
+
+        $this->assertFalse($result);
+    }
+
+    #[Test]
+    public function register_sets_source_to_third_party(): void
+    {
+        $this->provider->register_dashboard('ext-dashboard', [
+            'title'  => 'Extension',
+            'json'   => '{}',
+            'plugin' => 'My Plugin',
+        ]);
+
+        $this->assertTrue($this->provider->is_third_party('ext-dashboard'));
+    }
+
+    // ── get_available() ──────────────────────────────────────────────
+
+    #[Test]
+    public function get_available_includes_builtin_dashboards(): void
+    {
+        $fileExists = $this->getFunctionMock('Magdev\\WpPrometheus\\Admin', 'file_exists');
+        $fileExists->expects($this->any())->willReturn(true);
+
+        $available = $this->provider->get_available();
+
+        $this->assertArrayHasKey('wordpress-overview', $available);
+        $this->assertArrayHasKey('wordpress-runtime', $available);
+        $this->assertArrayHasKey('wordpress-woocommerce', $available);
+    }
+
+    #[Test]
+    public function get_available_includes_registered_dashboards(): void
+    {
+        $fileExists = $this->getFunctionMock('Magdev\\WpPrometheus\\Admin', 'file_exists');
+        $fileExists->expects($this->any())->willReturn(true);
+
+        $this->provider->register_dashboard('custom-dash', [
+            'title' => 'Custom',
+            'json'  => '{"panels":[]}',
+        ]);
+
+        $available = $this->provider->get_available();
+        $this->assertArrayHasKey('custom-dash', $available);
+    }
+
+    #[Test]
+    public function get_available_excludes_builtin_with_missing_file(): void
+    {
+        $fileExists = $this->getFunctionMock('Magdev\\WpPrometheus\\Admin', 'file_exists');
+        $fileExists->expects($this->any())->willReturn(false);
+
+        $available = $this->provider->get_available();
+
+        // Built-in dashboards should be excluded (files don't exist).
+        $this->assertArrayNotHasKey('wordpress-overview', $available);
+    }
+
+    // ── is_third_party() ─────────────────────────────────────────────
+
+    #[Test]
+    public function builtin_dashboard_is_not_third_party(): void
+    {
+        $this->assertFalse($this->provider->is_third_party('wordpress-overview'));
+    }
+
+    #[Test]
+    public function registered_dashboard_is_third_party(): void
+    {
+        $this->provider->register_dashboard('ext-dash', [
+            'title' => 'Extension Dashboard',
+            'json'  => '{}',
+        ]);
+
+        $this->assertTrue($this->provider->is_third_party('ext-dash'));
+    }
+
+    #[Test]
+    public function unknown_slug_is_not_third_party(): void
+    {
+        $this->assertFalse($this->provider->is_third_party('nonexistent'));
+    }
+
+    // ── get_plugin_name() ────────────────────────────────────────────
+
+    #[Test]
+    public function get_plugin_name_returns_name_for_registered(): void
+    {
+        $this->provider->register_dashboard('ext-dash', [
+            'title'  => 'Extension',
+            'json'   => '{}',
+            'plugin' => 'My Awesome Plugin',
+        ]);
+
+        $this->assertSame('My Awesome Plugin', $this->provider->get_plugin_name('ext-dash'));
+    }
+
+    #[Test]
+    public function get_plugin_name_returns_null_for_builtin(): void
+    {
+        $this->assertNull($this->provider->get_plugin_name('wordpress-overview'));
+    }
+
+    #[Test]
+    public function get_plugin_name_returns_null_when_empty(): void
+    {
+        $this->provider->register_dashboard('no-plugin', [
+            'title' => 'No Plugin',
+            'json'  => '{}',
+        ]);
+
+        $this->assertNull($this->provider->get_plugin_name('no-plugin'));
+    }
+
+    // ── get_filename() ───────────────────────────────────────────────
+
+    #[Test]
+    public function get_filename_returns_file_for_builtin(): void
+    {
+        $filename = $this->provider->get_filename('wordpress-overview');
+        $this->assertSame('wordpress-overview.json', $filename);
+    }
+
+    #[Test]
+    public function get_filename_returns_slug_json_for_inline(): void
+    {
+        $this->provider->register_dashboard('my-dash', [
+            'title' => 'My Dashboard',
+            'json'  => '{}',
+        ]);
+
+        $this->assertSame('my-dash.json', $this->provider->get_filename('my-dash'));
+    }
+
+    #[Test]
+    public function get_filename_returns_null_for_unknown(): void
+    {
+        $this->assertNull($this->provider->get_filename('nonexistent'));
+    }
+
+    // ── get_metadata() ───────────────────────────────────────────────
+
+    #[Test]
+    public function get_metadata_returns_builtin_data(): void
+    {
+        $metadata = $this->provider->get_metadata('wordpress-overview');
+
+        $this->assertIsArray($metadata);
+        $this->assertSame('WordPress Overview', $metadata['title']);
+        $this->assertSame('builtin', $metadata['source']);
+    }
+
+    #[Test]
+    public function get_metadata_returns_registered_data(): void
+    {
+        $this->provider->register_dashboard('ext-dash', [
+            'title'       => 'Extension',
+            'description' => 'A test dashboard',
+            'json'        => '{}',
+            'plugin'      => 'TestPlugin',
+        ]);
+
+        $metadata = $this->provider->get_metadata('ext-dash');
+
+        $this->assertIsArray($metadata);
+        $this->assertSame('Extension', $metadata['title']);
+        $this->assertSame('third-party', $metadata['source']);
+        $this->assertSame('TestPlugin', $metadata['plugin']);
+    }
+
+    #[Test]
+    public function get_metadata_returns_null_for_unknown(): void
+    {
+        $this->assertNull($this->provider->get_metadata('nonexistent'));
+    }
+}

tests/Unit/AuthenticationTest.php

@@ -0,0 +1,148 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Magdev\WpPrometheus\Tests\Unit;
+
+use Magdev\WpPrometheus\Tests\Helpers\GlobalFunctionState;
+use PHPUnit\Framework\Attributes\CoversFunction;
+use PHPUnit\Framework\Attributes\Test;
+
+#[CoversFunction('wp_prometheus_authenticate_request')]
+#[CoversFunction('wp_prometheus_get_authorization_header')]
+class AuthenticationTest extends TestCase
+{
+    private array $originalServer = [];
+    private array $originalGet = [];
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->originalServer = $_SERVER;
+        $this->originalGet = $_GET;
+    }
+
+    protected function tearDown(): void
+    {
+        $_SERVER = $this->originalServer;
+        $_GET = $this->originalGet;
+        parent::tearDown();
+    }
+
+    // ── wp_prometheus_authenticate_request() ─────────────────────────
+
+    #[Test]
+    public function returns_false_when_no_token_configured(): void
+    {
+        // No auth token in options → deny all.
+        $this->assertFalse(wp_prometheus_authenticate_request());
+    }
+
+    #[Test]
+    public function returns_false_when_token_is_empty_string(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_auth_token'] = '';
+        $this->assertFalse(wp_prometheus_authenticate_request());
+    }
+
+    #[Test]
+    public function bearer_token_authenticates_successfully(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_auth_token'] = 'secret-token-123';
+        $_SERVER['HTTP_AUTHORIZATION'] = 'Bearer secret-token-123';
+
+        $this->assertTrue(wp_prometheus_authenticate_request());
+    }
+
+    #[Test]
+    public function bearer_token_fails_with_wrong_token(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_auth_token'] = 'secret-token-123';
+        $_SERVER['HTTP_AUTHORIZATION'] = 'Bearer wrong-token';
+
+        $this->assertFalse(wp_prometheus_authenticate_request());
+    }
+
+    #[Test]
+    public function bearer_prefix_is_case_insensitive(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_auth_token'] = 'secret-token-123';
+        $_SERVER['HTTP_AUTHORIZATION'] = 'BEARER secret-token-123';
+
+        $this->assertTrue(wp_prometheus_authenticate_request());
+    }
+
+    #[Test]
+    public function query_parameter_authenticates_successfully(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_auth_token'] = 'secret-token-123';
+        $_GET['token'] = 'secret-token-123';
+
+        $this->assertTrue(wp_prometheus_authenticate_request());
+    }
+
+    #[Test]
+    public function query_parameter_fails_with_wrong_token(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_auth_token'] = 'secret-token-123';
+        $_GET['token'] = 'wrong-token';
+
+        $this->assertFalse(wp_prometheus_authenticate_request());
+    }
+
+    #[Test]
+    public function returns_false_when_no_auth_provided(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_auth_token'] = 'secret-token-123';
+        unset($_SERVER['HTTP_AUTHORIZATION'], $_SERVER['REDIRECT_HTTP_AUTHORIZATION']);
+        unset($_GET['token']);
+
+        $this->assertFalse(wp_prometheus_authenticate_request());
+    }
+
+    #[Test]
+    public function bearer_takes_precedence_over_query_parameter(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_auth_token'] = 'correct-token';
+        $_SERVER['HTTP_AUTHORIZATION'] = 'Bearer correct-token';
+        $_GET['token'] = 'wrong-token';
+
+        $this->assertTrue(wp_prometheus_authenticate_request());
+    }
+
+    // ── wp_prometheus_get_authorization_header() ─────────────────────
+
+    #[Test]
+    public function get_authorization_header_from_http_authorization(): void
+    {
+        $_SERVER['HTTP_AUTHORIZATION'] = 'Bearer my-token';
+
+        $this->assertSame('Bearer my-token', wp_prometheus_get_authorization_header());
+    }
+
+    #[Test]
+    public function get_authorization_header_from_redirect(): void
+    {
+        unset($_SERVER['HTTP_AUTHORIZATION']);
+        $_SERVER['REDIRECT_HTTP_AUTHORIZATION'] = 'Bearer redirect-token';
+
+        $this->assertSame('Bearer redirect-token', wp_prometheus_get_authorization_header());
+    }
+
+    #[Test]
+    public function get_authorization_header_returns_empty_when_absent(): void
+    {
+        unset($_SERVER['HTTP_AUTHORIZATION'], $_SERVER['REDIRECT_HTTP_AUTHORIZATION']);
+
+        $this->assertSame('', wp_prometheus_get_authorization_header());
+    }
+
+    #[Test]
+    public function http_authorization_takes_precedence_over_redirect(): void
+    {
+        $_SERVER['HTTP_AUTHORIZATION'] = 'Bearer primary';
+        $_SERVER['REDIRECT_HTTP_AUTHORIZATION'] = 'Bearer redirect';
+
+        $this->assertSame('Bearer primary', wp_prometheus_get_authorization_header());
+    }
+}

tests/Unit/Endpoint/MetricsEndpointTest.php

@@ -0,0 +1,102 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Magdev\WpPrometheus\Tests\Unit\Endpoint;
+
+use Magdev\WpPrometheus\Endpoint\MetricsEndpoint;
+use Magdev\WpPrometheus\Metrics\Collector;
+use Magdev\WpPrometheus\Metrics\StorageFactory;
+use Magdev\WpPrometheus\Tests\Helpers\GlobalFunctionState;
+use Magdev\WpPrometheus\Tests\Unit\TestCase;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\Test;
+
+#[CoversClass(MetricsEndpoint::class)]
+class MetricsEndpointTest extends TestCase
+{
+    private Collector $collector;
+    private MetricsEndpoint $endpoint;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->resetStorageFactory();
+        $this->collector = new Collector();
+        $this->endpoint = new MetricsEndpoint($this->collector);
+    }
+
+    protected function tearDown(): void
+    {
+        $this->resetStorageFactory();
+        parent::tearDown();
+    }
+
+    // ── Constructor ───────────────────────────────────────────────
+
+    #[Test]
+    public function constructor_accepts_collector(): void
+    {
+        $this->assertInstanceOf(MetricsEndpoint::class, $this->endpoint);
+    }
+
+    // ── register_endpoint() ───────────────────────────────────────
+
+    #[Test]
+    public function register_endpoint_adds_rewrite_rule(): void
+    {
+        $this->endpoint->register_endpoint();
+
+        $this->assertSame(1, GlobalFunctionState::getCallCount('add_rewrite_rule'));
+        $args = GlobalFunctionState::$callArgs['add_rewrite_rule'][0];
+        $this->assertSame('^metrics/?$', $args[0]);
+        $this->assertSame('index.php?wp_prometheus_metrics=1', $args[1]);
+        $this->assertSame('top', $args[2]);
+    }
+
+    #[Test]
+    public function register_endpoint_adds_rewrite_tag(): void
+    {
+        $this->endpoint->register_endpoint();
+
+        $this->assertSame(1, GlobalFunctionState::getCallCount('add_rewrite_tag'));
+        $args = GlobalFunctionState::$callArgs['add_rewrite_tag'][0];
+        $this->assertSame('%wp_prometheus_metrics%', $args[0]);
+        $this->assertSame('([^&]+)', $args[1]);
+    }
+
+    // ── handle_request() ──────────────────────────────────────────
+
+    #[Test]
+    public function handle_request_returns_early_when_no_query_var(): void
+    {
+        $wp = new \WP();
+        $wp->query_vars = [];
+
+        // Should return without calling exit or outputting anything.
+        $this->endpoint->handle_request($wp);
+
+        // If we reach this assertion, handle_request returned early (no exit).
+        $this->assertTrue(true);
+    }
+
+    #[Test]
+    public function handle_request_returns_early_when_query_var_empty(): void
+    {
+        $wp = new \WP();
+        $wp->query_vars = ['wp_prometheus_metrics' => ''];
+
+        $this->endpoint->handle_request($wp);
+
+        $this->assertTrue(true);
+    }
+
+    // ── Helpers ──────────────────────────────────────────────────
+
+    private function resetStorageFactory(): void
+    {
+        $reflection = new \ReflectionClass(StorageFactory::class);
+        $property = $reflection->getProperty('instance');
+        $property->setValue(null, null);
+    }
+}

tests/Unit/InstallerTest.php

@@ -0,0 +1,189 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Magdev\WpPrometheus\Tests\Unit;
+
+use Magdev\WpPrometheus\Installer;
+use Magdev\WpPrometheus\Tests\Helpers\GlobalFunctionState;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\Test;
+
+#[CoversClass(Installer::class)]
+class InstallerTest extends TestCase
+{
+    // ── activate() ───────────────────────────────────────────────────
+
+    #[Test]
+    public function activate_stores_activation_time(): void
+    {
+        Installer::activate();
+
+        $this->assertArrayHasKey(
+            'wp_prometheus_activated',
+            GlobalFunctionState::$options
+        );
+        $this->assertIsInt(GlobalFunctionState::$options['wp_prometheus_activated']);
+    }
+
+    #[Test]
+    public function activate_flushes_rewrite_rules(): void
+    {
+        Installer::activate();
+
+        $this->assertGreaterThanOrEqual(
+            1,
+            GlobalFunctionState::getCallCount('flush_rewrite_rules')
+        );
+    }
+
+    #[Test]
+    public function activate_generates_auth_token_when_not_set(): void
+    {
+        Installer::activate();
+
+        $this->assertArrayHasKey(
+            'wp_prometheus_auth_token',
+            GlobalFunctionState::$options
+        );
+        $this->assertNotEmpty(GlobalFunctionState::$options['wp_prometheus_auth_token']);
+    }
+
+    #[Test]
+    public function activate_preserves_existing_auth_token(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_auth_token'] = 'existing-token';
+
+        Installer::activate();
+
+        $this->assertSame(
+            'existing-token',
+            GlobalFunctionState::$options['wp_prometheus_auth_token']
+        );
+    }
+
+    #[Test]
+    public function activate_enables_default_metrics(): void
+    {
+        Installer::activate();
+
+        $this->assertSame(
+            1,
+            GlobalFunctionState::$options['wp_prometheus_enable_default_metrics']
+        );
+    }
+
+    #[Test]
+    public function activate_sets_default_enabled_metrics_list(): void
+    {
+        Installer::activate();
+
+        $enabled = GlobalFunctionState::$options['wp_prometheus_enabled_metrics'];
+        $this->assertIsArray($enabled);
+        $this->assertContains('wordpress_info', $enabled);
+        $this->assertContains('wordpress_users_total', $enabled);
+        $this->assertContains('wordpress_posts_total', $enabled);
+        $this->assertContains('wordpress_comments_total', $enabled);
+        $this->assertContains('wordpress_plugins_total', $enabled);
+    }
+
+    #[Test]
+    public function activate_preserves_existing_enabled_metrics(): void
+    {
+        $custom = ['wordpress_info', 'wordpress_users_total'];
+        GlobalFunctionState::$options['wp_prometheus_enabled_metrics'] = $custom;
+
+        Installer::activate();
+
+        $this->assertSame(
+            $custom,
+            GlobalFunctionState::$options['wp_prometheus_enabled_metrics']
+        );
+    }
+
+    // ── deactivate() ─────────────────────────────────────────────────
+
+    #[Test]
+    public function deactivate_flushes_rewrite_rules(): void
+    {
+        Installer::deactivate();
+
+        $this->assertGreaterThanOrEqual(
+            1,
+            GlobalFunctionState::getCallCount('flush_rewrite_rules')
+        );
+    }
+
+    // ── uninstall() ──────────────────────────────────────────────────
+
+    #[Test]
+    public function uninstall_removes_all_plugin_options(): void
+    {
+        // Set up options that should be cleaned.
+        $expected_options = [
+            'wp_prometheus_activated',
+            'wp_prometheus_license_key',
+            'wp_prometheus_license_server_url',
+            'wp_prometheus_license_server_secret',
+            'wp_prometheus_license_status',
+            'wp_prometheus_license_data',
+            'wp_prometheus_license_last_check',
+            'wp_prometheus_auth_token',
+            'wp_prometheus_enable_default_metrics',
+            'wp_prometheus_enabled_metrics',
+            'wp_prometheus_runtime_metrics',
+            'wp_prometheus_custom_metrics',
+            'wp_prometheus_isolated_mode',
+            'wp_prometheus_storage_adapter',
+            'wp_prometheus_redis_host',
+            'wp_prometheus_redis_port',
+            'wp_prometheus_redis_password',
+            'wp_prometheus_redis_database',
+            'wp_prometheus_redis_prefix',
+            'wp_prometheus_apcu_prefix',
+        ];
+
+        foreach ($expected_options as $option) {
+            GlobalFunctionState::$options[$option] = 'test_value';
+        }
+
+        Installer::uninstall();
+
+        // Verify all options were deleted.
+        foreach ($expected_options as $option) {
+            $this->assertArrayNotHasKey(
+                $option,
+                GlobalFunctionState::$options,
+                "Option '$option' was not deleted during uninstall"
+            );
+        }
+    }
+
+    #[Test]
+    public function uninstall_removes_license_transient(): void
+    {
+        Installer::uninstall();
+
+        $this->assertGreaterThanOrEqual(
+            1,
+            GlobalFunctionState::getCallCount('delete_transient')
+        );
+
+        // Verify the specific transient was targeted.
+        $args = GlobalFunctionState::$callArgs['delete_transient'] ?? [];
+        $transientNames = array_column($args, 0);
+        $this->assertContains('wp_prometheus_license_check', $transientNames);
+    }
+
+    #[Test]
+    public function uninstall_delete_option_call_count_matches(): void
+    {
+        Installer::uninstall();
+
+        // Should call delete_option for each option in the list (20 options).
+        $this->assertSame(
+            20,
+            GlobalFunctionState::getCallCount('delete_option')
+        );
+    }
+}

tests/Unit/Metrics/CollectorTest.php

@@ -0,0 +1,155 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Magdev\WpPrometheus\Tests\Unit\Metrics;
+
+use Magdev\WpPrometheus\Metrics\Collector;
+use Magdev\WpPrometheus\Metrics\RuntimeCollector;
+use Magdev\WpPrometheus\Metrics\StorageFactory;
+use Magdev\WpPrometheus\Tests\Unit\TestCase;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\Test;
+use Prometheus\CollectorRegistry;
+use Prometheus\Counter;
+use Prometheus\Gauge;
+use Prometheus\Histogram;
+
+#[CoversClass(Collector::class)]
+class CollectorTest extends TestCase
+{
+    private Collector $collector;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->resetStorageFactory();
+        $this->collector = new Collector();
+    }
+
+    protected function tearDown(): void
+    {
+        $this->resetRuntimeCollectorSingleton();
+        $this->resetStorageFactory();
+        parent::tearDown();
+    }
+
+    // ── Constructor & Basic Properties ─────────────────────────────
+
+    #[Test]
+    public function constructor_creates_registry(): void
+    {
+        $this->assertInstanceOf(CollectorRegistry::class, $this->collector->get_registry());
+    }
+
+    #[Test]
+    public function get_namespace_returns_wordpress(): void
+    {
+        $this->assertSame('wordpress', $this->collector->get_namespace());
+    }
+
+    // ── register_gauge() ──────────────────────────────────────────
+
+    #[Test]
+    public function register_gauge_returns_gauge_instance(): void
+    {
+        $gauge = $this->collector->register_gauge('test_metric', 'A test gauge');
+        $this->assertInstanceOf(Gauge::class, $gauge);
+    }
+
+    #[Test]
+    public function register_gauge_with_labels(): void
+    {
+        $gauge = $this->collector->register_gauge(
+            'labeled_metric',
+            'A labeled gauge',
+            ['label1', 'label2']
+        );
+        $this->assertInstanceOf(Gauge::class, $gauge);
+    }
+
+    // ── register_counter() ────────────────────────────────────────
+
+    #[Test]
+    public function register_counter_returns_counter_instance(): void
+    {
+        $counter = $this->collector->register_counter('test_counter', 'A test counter');
+        $this->assertInstanceOf(Counter::class, $counter);
+    }
+
+    #[Test]
+    public function register_counter_with_labels(): void
+    {
+        $counter = $this->collector->register_counter(
+            'labeled_counter',
+            'A labeled counter',
+            ['method', 'status']
+        );
+        $this->assertInstanceOf(Counter::class, $counter);
+    }
+
+    // ── register_histogram() ──────────────────────────────────────
+
+    #[Test]
+    public function register_histogram_returns_histogram_instance(): void
+    {
+        $histogram = $this->collector->register_histogram('test_histogram', 'A test histogram');
+        $this->assertInstanceOf(Histogram::class, $histogram);
+    }
+
+    #[Test]
+    public function register_histogram_with_custom_buckets(): void
+    {
+        $buckets = [0.1, 0.5, 1.0, 5.0];
+        $histogram = $this->collector->register_histogram(
+            'custom_buckets_hist',
+            'A histogram with custom buckets',
+            ['label1'],
+            $buckets
+        );
+        $this->assertInstanceOf(Histogram::class, $histogram);
+    }
+
+    // ── render() ──────────────────────────────────────────────────
+
+    #[Test]
+    public function render_returns_string(): void
+    {
+        $getOption = $this->getFunctionMock('Magdev\\WpPrometheus\\Metrics', 'get_option');
+        $getOption->expects($this->any())->willReturn([]);
+
+        $output = $this->collector->render();
+        $this->assertIsString($output);
+    }
+
+    #[Test]
+    public function render_includes_registered_gauge_value(): void
+    {
+        $getOption = $this->getFunctionMock('Magdev\\WpPrometheus\\Metrics', 'get_option');
+        $getOption->expects($this->any())->willReturn([]);
+
+        $gauge = $this->collector->register_gauge('test_render_metric', 'Test metric for render');
+        $gauge->set(42, []);
+
+        $output = $this->collector->render();
+
+        $this->assertStringContainsString('wordpress_test_render_metric', $output);
+        $this->assertStringContainsString('42', $output);
+    }
+
+    // ── Helpers ──────────────────────────────────────────────────
+
+    private function resetRuntimeCollectorSingleton(): void
+    {
+        $reflection = new \ReflectionClass(RuntimeCollector::class);
+        $property = $reflection->getProperty('instance');
+        $property->setValue(null, null);
+    }
+
+    private function resetStorageFactory(): void
+    {
+        $reflection = new \ReflectionClass(StorageFactory::class);
+        $property = $reflection->getProperty('instance');
+        $property->setValue(null, null);
+    }
+}

tests/Unit/Metrics/CustomMetricBuilderTest.php

@@ -0,0 +1,655 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Magdev\WpPrometheus\Tests\Unit\Metrics;
+
+use Magdev\WpPrometheus\Metrics\CustomMetricBuilder;
+use Magdev\WpPrometheus\Tests\Helpers\GlobalFunctionState;
+use Magdev\WpPrometheus\Tests\Unit\TestCase;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\Test;
+
+#[CoversClass(CustomMetricBuilder::class)]
+class CustomMetricBuilderTest extends TestCase
+{
+    private CustomMetricBuilder $builder;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->builder = new CustomMetricBuilder();
+    }
+
+    // ── validate_name() ──────────────────────────────────────────────
+
+    #[Test]
+    #[DataProvider('validMetricNamesProvider')]
+    public function validate_name_accepts_valid_names(string $name): void
+    {
+        $this->assertTrue($this->builder->validate_name($name));
+    }
+
+    public static function validMetricNamesProvider(): array
+    {
+        return [
+            'simple'                  => ['my_metric'],
+            'with_colon'              => ['my:metric'],
+            'starts_with_underscore'  => ['_private_metric'],
+            'starts_with_colon'       => [':special_metric'],
+            'uppercase'               => ['MY_METRIC'],
+            'mixed_case'              => ['myMetric123'],
+            'single_letter'           => ['m'],
+        ];
+    }
+
+    #[Test]
+    #[DataProvider('invalidMetricNamesProvider')]
+    public function validate_name_rejects_invalid_names(string $name): void
+    {
+        $this->assertFalse($this->builder->validate_name($name));
+    }
+
+    public static function invalidMetricNamesProvider(): array
+    {
+        return [
+            'starts_with_digit' => ['0metric'],
+            'contains_dash'     => ['my-metric'],
+            'contains_space'    => ['my metric'],
+            'contains_dot'      => ['my.metric'],
+            'empty_string'      => [''],
+            'special_chars'     => ['metric@name'],
+        ];
+    }
+
+    // ── validate_label_name() ────────────────────────────────────────
+
+    #[Test]
+    #[DataProvider('validLabelNamesProvider')]
+    public function validate_label_name_accepts_valid_names(string $name): void
+    {
+        $this->assertTrue($this->builder->validate_label_name($name));
+    }
+
+    public static function validLabelNamesProvider(): array
+    {
+        return [
+            'simple'                 => ['status'],
+            'with_underscore'        => ['http_method'],
+            'starts_with_underscore' => ['_internal'],
+            'uppercase'              => ['METHOD'],
+            'alphanumeric'           => ['label1'],
+        ];
+    }
+
+    #[Test]
+    #[DataProvider('invalidLabelNamesProvider')]
+    public function validate_label_name_rejects_invalid_names(string $name): void
+    {
+        $this->assertFalse($this->builder->validate_label_name($name));
+    }
+
+    public static function invalidLabelNamesProvider(): array
+    {
+        return [
+            'double_underscore_prefix' => ['__reserved'],
+            'starts_with_digit'        => ['1label'],
+            'contains_colon'           => ['label:name'],
+            'contains_dash'            => ['label-name'],
+            'empty_string'             => [''],
+            'contains_space'           => ['label name'],
+        ];
+    }
+
+    // ── validate() ───────────────────────────────────────────────────
+
+    #[Test]
+    public function validate_returns_empty_for_valid_metric(): void
+    {
+        $errors = $this->builder->validate($this->validMetric());
+        $this->assertEmpty($errors);
+    }
+
+    #[Test]
+    public function validate_requires_name(): void
+    {
+        $metric = $this->validMetric();
+        $metric['name'] = '';
+
+        $errors = $this->builder->validate($metric);
+        $this->assertNotEmpty($errors);
+        $this->assertStringContainsString('name is required', $errors[0]);
+    }
+
+    #[Test]
+    public function validate_rejects_invalid_metric_name(): void
+    {
+        $metric = $this->validMetric();
+        $metric['name'] = '0invalid';
+
+        $errors = $this->builder->validate($metric);
+        $this->assertNotEmpty($errors);
+        $this->assertStringContainsString('must start with', $errors[0]);
+    }
+
+    #[Test]
+    #[DataProvider('reservedPrefixProvider')]
+    public function validate_rejects_reserved_prefix(string $prefix): void
+    {
+        $metric = $this->validMetric();
+        $metric['name'] = $prefix . 'test';
+
+        $errors = $this->builder->validate($metric);
+        $this->assertNotEmpty($errors);
+        $this->assertStringContainsString('reserved prefix', implode(' ', $errors));
+    }
+
+    public static function reservedPrefixProvider(): array
+    {
+        return [
+            'wordpress_' => ['wordpress_'],
+            'go_'        => ['go_'],
+            'process_'   => ['process_'],
+            'promhttp_'  => ['promhttp_'],
+        ];
+    }
+
+    #[Test]
+    public function validate_detects_duplicate_name(): void
+    {
+        GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME] = [
+            'existing-id' => [
+                'id'   => 'existing-id',
+                'name' => 'custom_existing',
+                'help' => 'test',
+            ],
+        ];
+
+        $metric = $this->validMetric();
+        $metric['name'] = 'custom_existing';
+
+        $errors = $this->builder->validate($metric);
+        $this->assertNotEmpty($errors);
+        $this->assertStringContainsString('already exists', implode(' ', $errors));
+    }
+
+    #[Test]
+    public function validate_allows_same_name_when_editing(): void
+    {
+        GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME] = [
+            'my-id' => [
+                'id'   => 'my-id',
+                'name' => 'custom_existing',
+                'help' => 'test',
+            ],
+        ];
+
+        $metric = $this->validMetric();
+        $metric['id'] = 'my-id';
+        $metric['name'] = 'custom_existing';
+
+        $errors = $this->builder->validate($metric);
+        $this->assertEmpty($errors);
+    }
+
+    #[Test]
+    public function validate_requires_help_text(): void
+    {
+        $metric = $this->validMetric();
+        $metric['help'] = '';
+
+        $errors = $this->builder->validate($metric);
+        $this->assertNotEmpty($errors);
+        $this->assertStringContainsString('Help text is required', $errors[0]);
+    }
+
+    #[Test]
+    public function validate_requires_valid_type(): void
+    {
+        $metric = $this->validMetric();
+        $metric['type'] = 'counter';
+
+        $errors = $this->builder->validate($metric);
+        $this->assertNotEmpty($errors);
+        $this->assertStringContainsString('Invalid metric type', implode(' ', $errors));
+    }
+
+    #[Test]
+    public function validate_rejects_too_many_labels(): void
+    {
+        $metric = $this->validMetric();
+        $metric['labels'] = ['a', 'b', 'c', 'd', 'e', 'f'];
+
+        $errors = $this->builder->validate($metric);
+        $this->assertNotEmpty($errors);
+        $this->assertStringContainsString('Maximum', implode(' ', $errors));
+    }
+
+    #[Test]
+    public function validate_rejects_invalid_label_names_in_array(): void
+    {
+        $metric = $this->validMetric();
+        $metric['labels'] = ['valid', '__reserved'];
+
+        $errors = $this->builder->validate($metric);
+        $this->assertNotEmpty($errors);
+        $this->assertStringContainsString('Invalid label name', implode(' ', $errors));
+    }
+
+    #[Test]
+    public function validate_rejects_non_array_labels(): void
+    {
+        $metric = $this->validMetric();
+        $metric['labels'] = 'not_an_array';
+
+        $errors = $this->builder->validate($metric);
+        $this->assertNotEmpty($errors);
+        $this->assertStringContainsString('Labels must be an array', implode(' ', $errors));
+    }
+
+    #[Test]
+    public function validate_requires_valid_value_type(): void
+    {
+        $metric = $this->validMetric();
+        $metric['value_type'] = 'invalid';
+
+        $errors = $this->builder->validate($metric);
+        $this->assertNotEmpty($errors);
+        $this->assertStringContainsString('Invalid value type', implode(' ', $errors));
+    }
+
+    #[Test]
+    public function validate_requires_option_name_for_option_type(): void
+    {
+        $metric = $this->validMetric();
+        $metric['value_type'] = 'option';
+        $metric['value_config'] = [];
+
+        $errors = $this->builder->validate($metric);
+        $this->assertNotEmpty($errors);
+        $this->assertStringContainsString('Option name is required', implode(' ', $errors));
+    }
+
+    #[Test]
+    public function validate_accepts_option_type_with_option_name(): void
+    {
+        $metric = $this->validMetric();
+        $metric['value_type'] = 'option';
+        $metric['value_config'] = ['option_name' => 'my_wp_option'];
+
+        $errors = $this->builder->validate($metric);
+        $this->assertEmpty($errors);
+    }
+
+    #[Test]
+    public function validate_rejects_too_many_label_values(): void
+    {
+        $metric = $this->validMetric();
+        $metric['labels'] = ['status'];
+        $metric['label_values'] = array_fill(0, 51, ['active', 1.0]);
+
+        $errors = $this->builder->validate($metric);
+        $this->assertNotEmpty($errors);
+        $this->assertStringContainsString('Maximum', implode(' ', $errors));
+    }
+
+    #[Test]
+    public function validate_checks_label_value_row_count(): void
+    {
+        $metric = $this->validMetric();
+        $metric['labels'] = ['status', 'type'];
+        // Row has 2 items but needs 3 (2 labels + 1 value).
+        $metric['label_values'] = [['active', 1.0]];
+
+        $errors = $this->builder->validate($metric);
+        $this->assertNotEmpty($errors);
+        $this->assertStringContainsString('values for all labels', implode(' ', $errors));
+    }
+
+    // ── get_all() / get() ────────────────────────────────────────────
+
+    #[Test]
+    public function get_all_returns_empty_array_by_default(): void
+    {
+        $this->assertSame([], $this->builder->get_all());
+    }
+
+    #[Test]
+    public function get_all_returns_stored_metrics(): void
+    {
+        $metrics = ['id1' => ['name' => 'test_metric']];
+        GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME] = $metrics;
+
+        $this->assertSame($metrics, $this->builder->get_all());
+    }
+
+    #[Test]
+    public function get_all_returns_empty_when_option_is_not_array(): void
+    {
+        GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME] = 'not_an_array';
+        $this->assertSame([], $this->builder->get_all());
+    }
+
+    #[Test]
+    public function get_returns_metric_by_id(): void
+    {
+        $metric = ['id' => 'my-id', 'name' => 'test_metric', 'help' => 'Test'];
+        GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME] = ['my-id' => $metric];
+
+        $this->assertSame($metric, $this->builder->get('my-id'));
+    }
+
+    #[Test]
+    public function get_returns_null_for_nonexistent_id(): void
+    {
+        $this->assertNull($this->builder->get('nonexistent'));
+    }
+
+    // ── save() ───────────────────────────────────────────────────────
+
+    #[Test]
+    public function save_creates_new_metric_and_returns_id(): void
+    {
+        $metric = $this->validMetric();
+        $id = $this->builder->save($metric);
+
+        $this->assertNotEmpty($id);
+        $this->assertGreaterThanOrEqual(1, GlobalFunctionState::getCallCount('update_option'));
+
+        $saved = GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME];
+        $this->assertArrayHasKey($id, $saved);
+        $this->assertSame('custom_test_metric', $saved[$id]['name']);
+    }
+
+    #[Test]
+    public function save_throws_on_validation_failure(): void
+    {
+        $metric = [
+            'name'       => '',
+            'help'       => '',
+            'type'       => 'gauge',
+            'value_type' => 'static',
+        ];
+
+        $this->expectException(\InvalidArgumentException::class);
+        $this->builder->save($metric);
+    }
+
+    #[Test]
+    public function save_updates_existing_metric(): void
+    {
+        GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME] = [
+            'existing-id' => [
+                'id'         => 'existing-id',
+                'name'       => 'custom_test_metric',
+                'help'       => 'Original help',
+                'type'       => 'gauge',
+                'value_type' => 'static',
+                'labels'     => [],
+                'created_at' => 1000000,
+            ],
+        ];
+
+        $metric = $this->validMetric();
+        $metric['id'] = 'existing-id';
+        $metric['help'] = 'Updated help';
+
+        $id = $this->builder->save($metric);
+
+        $this->assertSame('existing-id', $id);
+        $saved = GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME];
+        $this->assertSame('Updated help', $saved['existing-id']['help']);
+    }
+
+    #[Test]
+    public function save_sanitizes_metric_data(): void
+    {
+        $metric = $this->validMetric();
+        $metric['labels'] = ['valid_label'];
+        $metric['label_values'] = [['active', 42.5]];
+
+        $id = $this->builder->save($metric);
+        $saved = GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME][$id];
+
+        $this->assertSame(['valid_label'], $saved['labels']);
+        $this->assertSame([['active', 42.5]], $saved['label_values']);
+        $this->assertIsBool($saved['enabled']);
+    }
+
+    // ── delete() ─────────────────────────────────────────────────────
+
+    #[Test]
+    public function delete_removes_metric(): void
+    {
+        GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME] = [
+            'my-id' => ['id' => 'my-id', 'name' => 'custom_metric'],
+        ];
+
+        $this->assertTrue($this->builder->delete('my-id'));
+        $this->assertArrayNotHasKey(
+            'my-id',
+            GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME]
+        );
+    }
+
+    #[Test]
+    public function delete_returns_false_for_nonexistent(): void
+    {
+        $this->assertFalse($this->builder->delete('nonexistent'));
+    }
+
+    // ── export() ─────────────────────────────────────────────────────
+
+    #[Test]
+    public function export_returns_valid_json_with_metadata(): void
+    {
+        GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME] = [
+            'id1' => ['name' => 'metric1', 'help' => 'Test 1'],
+        ];
+
+        $json = $this->builder->export();
+        $data = json_decode($json, true);
+
+        $this->assertIsArray($data);
+        $this->assertSame(CustomMetricBuilder::EXPORT_VERSION, $data['version']);
+        $this->assertSame(WP_PROMETHEUS_VERSION, $data['plugin_version']);
+        $this->assertArrayHasKey('exported_at', $data);
+        $this->assertCount(1, $data['metrics']);
+    }
+
+    #[Test]
+    public function export_does_not_include_site_url(): void
+    {
+        GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME] = [];
+
+        $json = $this->builder->export();
+        $data = json_decode($json, true);
+
+        $this->assertArrayNotHasKey('site_url', $data);
+    }
+
+    // ── import() ─────────────────────────────────────────────────────
+
+    #[Test]
+    public function import_rejects_oversized_json(): void
+    {
+        $json = str_repeat('x', CustomMetricBuilder::MAX_IMPORT_SIZE + 1);
+
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('exceeds maximum size');
+        $this->builder->import($json);
+    }
+
+    #[Test]
+    public function import_rejects_invalid_json(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Invalid JSON');
+        $this->builder->import('{invalid json');
+    }
+
+    #[Test]
+    public function import_rejects_missing_metrics_key(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('No metrics found');
+        $this->builder->import('{"version":"1.0.0"}');
+    }
+
+    #[Test]
+    public function import_skip_mode_skips_duplicates(): void
+    {
+        GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME] = [
+            'existing' => [
+                'id'   => 'existing',
+                'name' => 'custom_existing_metric',
+                'help' => 'Test',
+            ],
+        ];
+
+        $json = json_encode([
+            'version' => '1.0.0',
+            'metrics' => [
+                [
+                    'name'       => 'custom_existing_metric',
+                    'help'       => 'Test',
+                    'type'       => 'gauge',
+                    'value_type' => 'static',
+                ],
+            ],
+        ]);
+
+        $result = $this->builder->import($json, 'skip');
+        $this->assertSame(1, $result['skipped']);
+        $this->assertSame(0, $result['imported']);
+    }
+
+    #[Test]
+    public function import_rename_mode_renames_duplicates(): void
+    {
+        GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME] = [
+            'existing' => [
+                'id'         => 'existing',
+                'name'       => 'custom_existing_metric',
+                'help'       => 'Existing',
+                'type'       => 'gauge',
+                'value_type' => 'static',
+                'labels'     => [],
+            ],
+        ];
+
+        $json = json_encode([
+            'version' => '1.0.0',
+            'metrics' => [
+                [
+                    'name'       => 'custom_existing_metric',
+                    'help'       => 'Imported',
+                    'type'       => 'gauge',
+                    'value_type' => 'static',
+                    'labels'     => [],
+                ],
+            ],
+        ]);
+
+        $result = $this->builder->import($json, 'rename');
+        $this->assertSame(1, $result['imported']);
+
+        $all = $this->builder->get_all();
+        $names = array_column($all, 'name');
+        $this->assertContains('custom_existing_metric', $names);
+        $this->assertContains('custom_existing_metric_imported_1', $names);
+    }
+
+    #[Test]
+    public function import_invalid_mode_defaults_to_skip(): void
+    {
+        GlobalFunctionState::$options[CustomMetricBuilder::OPTION_NAME] = [
+            'existing' => [
+                'id'   => 'existing',
+                'name' => 'custom_existing_metric',
+                'help' => 'Test',
+            ],
+        ];
+
+        $json = json_encode([
+            'version' => '1.0.0',
+            'metrics' => [
+                [
+                    'name'       => 'custom_existing_metric',
+                    'help'       => 'Test',
+                    'type'       => 'gauge',
+                    'value_type' => 'static',
+                ],
+            ],
+        ]);
+
+        $result = $this->builder->import($json, 'invalid_mode');
+        $this->assertSame(1, $result['skipped']);
+    }
+
+    #[Test]
+    public function import_counts_metrics_without_name_as_errors(): void
+    {
+        $json = json_encode([
+            'version' => '1.0.0',
+            'metrics' => [['help' => 'No name']],
+        ]);
+
+        $result = $this->builder->import($json);
+        $this->assertSame(1, $result['errors']);
+        $this->assertSame(0, $result['imported']);
+    }
+
+    #[Test]
+    public function import_successfully_imports_new_metric(): void
+    {
+        $json = json_encode([
+            'version' => '1.0.0',
+            'metrics' => [
+                [
+                    'name'       => 'custom_new_metric',
+                    'help'       => 'A new metric',
+                    'type'       => 'gauge',
+                    'value_type' => 'static',
+                    'labels'     => [],
+                ],
+            ],
+        ]);
+
+        $result = $this->builder->import($json);
+        $this->assertSame(1, $result['imported']);
+        $this->assertSame(0, $result['skipped']);
+        $this->assertSame(0, $result['errors']);
+
+        $all = $this->builder->get_all();
+        $names = array_column($all, 'name');
+        $this->assertContains('custom_new_metric', $names);
+    }
+
+    // ── Constants ────────────────────────────────────────────────────
+
+    #[Test]
+    public function constants_are_defined(): void
+    {
+        $this->assertSame('wp_prometheus_custom_metrics', CustomMetricBuilder::OPTION_NAME);
+        $this->assertSame(5, CustomMetricBuilder::MAX_LABELS);
+        $this->assertSame(50, CustomMetricBuilder::MAX_LABEL_VALUES);
+        $this->assertSame(1048576, CustomMetricBuilder::MAX_IMPORT_SIZE);
+    }
+
+    // ── Helpers ──────────────────────────────────────────────────────
+
+    private function validMetric(): array
+    {
+        return [
+            'name'         => 'custom_test_metric',
+            'help'         => 'A test metric',
+            'type'         => 'gauge',
+            'value_type'   => 'static',
+            'labels'       => [],
+            'label_values' => [],
+            'enabled'      => true,
+        ];
+    }
+}

tests/Unit/Metrics/RuntimeCollectorTest.php

@@ -0,0 +1,234 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Magdev\WpPrometheus\Tests\Unit\Metrics;
+
+use Magdev\WpPrometheus\Metrics\RuntimeCollector;
+use Magdev\WpPrometheus\Tests\Helpers\GlobalFunctionState;
+use Magdev\WpPrometheus\Tests\Unit\TestCase;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\Test;
+
+#[CoversClass(RuntimeCollector::class)]
+class RuntimeCollectorTest extends TestCase
+{
+    private RuntimeCollector $collector;
+    private array $originalServer = [];
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->originalServer = $_SERVER;
+        $this->collector = $this->createInstance();
+    }
+
+    protected function tearDown(): void
+    {
+        $_SERVER = $this->originalServer;
+        $this->resetSingleton();
+        parent::tearDown();
+    }
+
+    // ── Singleton ────────────────────────────────────────────────────
+
+    #[Test]
+    public function get_instance_returns_singleton(): void
+    {
+        $instance1 = RuntimeCollector::get_instance();
+        $instance2 = RuntimeCollector::get_instance();
+
+        $this->assertSame($instance1, $instance2);
+    }
+
+    #[Test]
+    public function get_instance_returns_runtime_collector(): void
+    {
+        $instance = RuntimeCollector::get_instance();
+        $this->assertInstanceOf(RuntimeCollector::class, $instance);
+    }
+
+    // ── get_stored_metrics() ─────────────────────────────────────────
+
+    #[Test]
+    public function get_stored_metrics_returns_default_when_empty(): void
+    {
+        $metrics = $this->collector->get_stored_metrics();
+        $this->assertSame([], $metrics);
+    }
+
+    #[Test]
+    public function get_stored_metrics_returns_stored_data(): void
+    {
+        $stored = [
+            'counters'   => ['key' => ['name' => 'test', 'value' => 5]],
+            'histograms' => [],
+            'last_reset' => 1000000,
+        ];
+        GlobalFunctionState::$options['wp_prometheus_runtime_metrics'] = $stored;
+
+        $metrics = $this->collector->get_stored_metrics();
+        $this->assertSame($stored, $metrics);
+    }
+
+    #[Test]
+    public function get_stored_metrics_returns_default_for_non_array(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_runtime_metrics'] = 'invalid';
+
+        $metrics = $this->collector->get_stored_metrics();
+        $this->assertArrayHasKey('counters', $metrics);
+        $this->assertArrayHasKey('histograms', $metrics);
+        $this->assertArrayHasKey('last_reset', $metrics);
+    }
+
+    // ── reset_metrics() ──────────────────────────────────────────────
+
+    #[Test]
+    public function reset_metrics_deletes_option(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_runtime_metrics'] = ['data'];
+
+        RuntimeCollector::reset_metrics();
+
+        $this->assertSame(1, GlobalFunctionState::getCallCount('delete_option'));
+        $this->assertArrayNotHasKey(
+            'wp_prometheus_runtime_metrics',
+            GlobalFunctionState::$options
+        );
+    }
+
+    // ── get_duration_buckets() ───────────────────────────────────────
+
+    #[Test]
+    public function get_duration_buckets_returns_expected_values(): void
+    {
+        $buckets = RuntimeCollector::get_duration_buckets();
+
+        $this->assertIsArray($buckets);
+        $this->assertCount(11, $buckets);
+        $this->assertSame(0.005, $buckets[0]);
+        $this->assertEquals(10, end($buckets));
+    }
+
+    #[Test]
+    public function duration_buckets_are_in_ascending_order(): void
+    {
+        $buckets = RuntimeCollector::get_duration_buckets();
+        $sorted = $buckets;
+        sort($sorted);
+
+        $this->assertSame($sorted, $buckets);
+    }
+
+    // ── get_normalized_endpoint() (private, via reflection) ──────────
+
+    #[Test]
+    public function normalized_endpoint_returns_admin_when_is_admin(): void
+    {
+        $_SERVER['REQUEST_URI'] = '/wp-admin/options-general.php';
+        GlobalFunctionState::$options['__is_admin'] = true;
+
+        $result = $this->callPrivateMethod('get_normalized_endpoint');
+        $this->assertSame('admin', $result);
+    }
+
+    #[Test]
+    public function normalized_endpoint_returns_ajax_when_doing_ajax(): void
+    {
+        $_SERVER['REQUEST_URI'] = '/wp-admin/admin-ajax.php';
+        GlobalFunctionState::$options['__wp_doing_ajax'] = true;
+
+        $result = $this->callPrivateMethod('get_normalized_endpoint');
+        $this->assertSame('ajax', $result);
+    }
+
+    #[Test]
+    public function normalized_endpoint_returns_cron_when_doing_cron(): void
+    {
+        // Use a generic URI (not /wp-cron.php) to ensure function is checked, not URL pattern.
+        $_SERVER['REQUEST_URI'] = '/some-page';
+        GlobalFunctionState::$options['__wp_doing_cron'] = true;
+
+        $result = $this->callPrivateMethod('get_normalized_endpoint');
+        $this->assertSame('cron', $result);
+    }
+
+    #[Test]
+    #[DataProvider('urlEndpointProvider')]
+    public function normalized_endpoint_from_url_pattern(string $uri, string $expected): void
+    {
+        $_SERVER['REQUEST_URI'] = $uri;
+
+        $result = $this->callPrivateMethod('get_normalized_endpoint');
+        $this->assertSame($expected, $result);
+    }
+
+    public static function urlEndpointProvider(): array
+    {
+        return [
+            'rest api'         => ['/wp-json/wp/v2/posts', 'rest-api'],
+            'login page'       => ['/wp-login.php', 'login'],
+            'login with query' => ['/wp-login.php?action=login', 'login'],
+            'wp-cron'          => ['/wp-cron.php', 'cron'],
+            'feed root'        => ['/feed/', 'feed'],
+            'feed trailing'    => ['/category/news/feed', 'feed'],
+            'feed with slash'  => ['/feed', 'feed'],
+            'homepage'         => ['/', 'frontend'],
+            'page'             => ['/about-us', 'frontend'],
+            'post'             => ['/2024/01/hello-world', 'frontend'],
+        ];
+    }
+
+    // ── is_metrics_request() (private, via reflection) ───────────────
+
+    #[Test]
+    public function is_metrics_request_true_for_metrics_uri(): void
+    {
+        $_SERVER['REQUEST_URI'] = '/metrics';
+        $this->assertTrue($this->callPrivateMethod('is_metrics_request'));
+    }
+
+    #[Test]
+    public function is_metrics_request_true_with_trailing_slash(): void
+    {
+        $_SERVER['REQUEST_URI'] = '/metrics/';
+        $this->assertTrue($this->callPrivateMethod('is_metrics_request'));
+    }
+
+    #[Test]
+    public function is_metrics_request_false_for_other_uri(): void
+    {
+        $_SERVER['REQUEST_URI'] = '/some-page';
+        $this->assertFalse($this->callPrivateMethod('is_metrics_request'));
+    }
+
+    #[Test]
+    public function is_metrics_request_false_when_no_uri(): void
+    {
+        unset($_SERVER['REQUEST_URI']);
+        $this->assertFalse($this->callPrivateMethod('is_metrics_request'));
+    }
+
+    // ── Helpers ──────────────────────────────────────────────────────
+
+    private function createInstance(): RuntimeCollector
+    {
+        $reflection = new \ReflectionClass(RuntimeCollector::class);
+        return $reflection->newInstanceWithoutConstructor();
+    }
+
+    private function resetSingleton(): void
+    {
+        $reflection = new \ReflectionClass(RuntimeCollector::class);
+        $property = $reflection->getProperty('instance');
+        $property->setValue(null, null);
+    }
+
+    private function callPrivateMethod(string $method, array $args = []): mixed
+    {
+        $reflection = new \ReflectionMethod($this->collector, $method);
+        return $reflection->invoke($this->collector, ...$args);
+    }
+}

tests/Unit/Metrics/StorageFactoryTest.php

@@ -0,0 +1,411 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Magdev\WpPrometheus\Tests\Unit\Metrics;
+
+use Magdev\WpPrometheus\Metrics\StorageFactory;
+use Magdev\WpPrometheus\Tests\Helpers\GlobalFunctionState;
+use Magdev\WpPrometheus\Tests\Unit\TestCase;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\Test;
+use Prometheus\Storage\InMemory;
+
+#[CoversClass(StorageFactory::class)]
+class StorageFactoryTest extends TestCase
+{
+    /** @var list<string> Environment variables to clean up after each test. */
+    private array $envVarsToClean = [];
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        StorageFactory::reset();
+    }
+
+    protected function tearDown(): void
+    {
+        StorageFactory::reset();
+        foreach ($this->envVarsToClean as $var) {
+            putenv($var);
+        }
+        $this->envVarsToClean = [];
+        parent::tearDown();
+    }
+
+    // ── Adapter Constants ────────────────────────────────────────────
+
+    #[Test]
+    public function adapter_constants_are_defined(): void
+    {
+        $this->assertSame('inmemory', StorageFactory::ADAPTER_INMEMORY);
+        $this->assertSame('redis', StorageFactory::ADAPTER_REDIS);
+        $this->assertSame('apcu', StorageFactory::ADAPTER_APCU);
+    }
+
+    // ── get_available_adapters() ─────────────────────────────────────
+
+    #[Test]
+    public function get_available_adapters_returns_all_three(): void
+    {
+        $adapters = StorageFactory::get_available_adapters();
+
+        $this->assertArrayHasKey(StorageFactory::ADAPTER_INMEMORY, $adapters);
+        $this->assertArrayHasKey(StorageFactory::ADAPTER_REDIS, $adapters);
+        $this->assertArrayHasKey(StorageFactory::ADAPTER_APCU, $adapters);
+        $this->assertCount(3, $adapters);
+    }
+
+    // ── is_adapter_available() ───────────────────────────────────────
+
+    #[Test]
+    public function inmemory_adapter_is_always_available(): void
+    {
+        $this->assertTrue(StorageFactory::is_adapter_available(StorageFactory::ADAPTER_INMEMORY));
+    }
+
+    #[Test]
+    public function unknown_adapter_is_not_available(): void
+    {
+        $this->assertFalse(StorageFactory::is_adapter_available('unknown'));
+    }
+
+    #[Test]
+    public function redis_availability_depends_on_extension(): void
+    {
+        $extensionLoaded = $this->getFunctionMock(
+            'Magdev\\WpPrometheus\\Metrics',
+            'extension_loaded'
+        );
+        $extensionLoaded->expects($this->any())->willReturn(false);
+
+        $this->assertFalse(StorageFactory::is_adapter_available(StorageFactory::ADAPTER_REDIS));
+    }
+
+    #[Test]
+    public function apcu_availability_requires_extension_and_enabled(): void
+    {
+        $extensionLoaded = $this->getFunctionMock(
+            'Magdev\\WpPrometheus\\Metrics',
+            'extension_loaded'
+        );
+        $extensionLoaded->expects($this->any())->willReturn(true);
+
+        $apcuEnabled = $this->getFunctionMock(
+            'Magdev\\WpPrometheus\\Metrics',
+            'apcu_enabled'
+        );
+        $apcuEnabled->expects($this->any())->willReturn(false);
+
+        $this->assertFalse(StorageFactory::is_adapter_available(StorageFactory::ADAPTER_APCU));
+    }
+
+    // ── get_configured_adapter() ─────────────────────────────────────
+
+    #[Test]
+    public function default_configured_adapter_is_inmemory(): void
+    {
+        $this->assertSame('inmemory', StorageFactory::get_configured_adapter());
+    }
+
+    #[Test]
+    public function configured_adapter_reads_from_env_var(): void
+    {
+        $this->setEnv('WP_PROMETHEUS_STORAGE_ADAPTER', 'redis');
+
+        $this->assertSame('redis', StorageFactory::get_configured_adapter());
+    }
+
+    #[Test]
+    public function configured_adapter_reads_from_option(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_storage_adapter'] = 'apcu';
+
+        $this->assertSame('apcu', StorageFactory::get_configured_adapter());
+    }
+
+    #[Test]
+    public function env_var_takes_precedence_over_option(): void
+    {
+        $this->setEnv('WP_PROMETHEUS_STORAGE_ADAPTER', 'redis');
+        GlobalFunctionState::$options['wp_prometheus_storage_adapter'] = 'apcu';
+
+        $this->assertSame('redis', StorageFactory::get_configured_adapter());
+    }
+
+    #[Test]
+    public function configured_adapter_lowercases_env_value(): void
+    {
+        $this->setEnv('WP_PROMETHEUS_STORAGE_ADAPTER', 'REDIS');
+
+        $this->assertSame('redis', StorageFactory::get_configured_adapter());
+    }
+
+    // ── get_redis_config() ───────────────────────────────────────────
+
+    #[Test]
+    public function get_redis_config_returns_defaults(): void
+    {
+        $config = StorageFactory::get_redis_config();
+
+        $this->assertSame('127.0.0.1', $config['host']);
+        $this->assertSame(6379, $config['port']);
+        $this->assertSame('', $config['password']);
+        $this->assertSame(0, $config['database']);
+        $this->assertSame('WORDPRESS_PROMETHEUS_', $config['prefix']);
+    }
+
+    #[Test]
+    public function get_redis_config_reads_from_env_vars(): void
+    {
+        $this->setEnv('WP_PROMETHEUS_REDIS_HOST', '10.0.0.1');
+        $this->setEnv('WP_PROMETHEUS_REDIS_PORT', '6380');
+        $this->setEnv('WP_PROMETHEUS_REDIS_PASSWORD', 's3cret');
+        $this->setEnv('WP_PROMETHEUS_REDIS_DATABASE', '2');
+        $this->setEnv('WP_PROMETHEUS_REDIS_PREFIX', 'MY_PREFIX_');
+
+        $config = StorageFactory::get_redis_config();
+
+        $this->assertSame('10.0.0.1', $config['host']);
+        $this->assertSame(6380, $config['port']);
+        $this->assertSame('s3cret', $config['password']);
+        $this->assertSame(2, $config['database']);
+        $this->assertSame('MY_PREFIX_', $config['prefix']);
+    }
+
+    #[Test]
+    public function get_redis_config_reads_from_option(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_redis_config'] = [
+            'host'     => '192.168.1.1',
+            'port'     => 6381,
+            'password' => 'optpass',
+            'database' => 3,
+            'prefix'   => 'OPT_',
+        ];
+
+        $config = StorageFactory::get_redis_config();
+
+        $this->assertSame('192.168.1.1', $config['host']);
+        $this->assertSame(6381, $config['port']);
+        $this->assertSame('optpass', $config['password']);
+        $this->assertSame(3, $config['database']);
+        $this->assertSame('OPT_', $config['prefix']);
+    }
+
+    #[Test]
+    public function get_redis_config_env_takes_precedence(): void
+    {
+        $this->setEnv('WP_PROMETHEUS_REDIS_HOST', 'env-host');
+        GlobalFunctionState::$options['wp_prometheus_redis_config'] = [
+            'host' => 'option-host',
+        ];
+
+        $config = StorageFactory::get_redis_config();
+        $this->assertSame('env-host', $config['host']);
+    }
+
+    // ── get_apcu_prefix() ────────────────────────────────────────────
+
+    #[Test]
+    public function get_apcu_prefix_returns_default(): void
+    {
+        $this->assertSame('wp_prom', StorageFactory::get_apcu_prefix());
+    }
+
+    #[Test]
+    public function get_apcu_prefix_reads_from_env(): void
+    {
+        $this->setEnv('WP_PROMETHEUS_APCU_PREFIX', 'custom_prefix');
+
+        $this->assertSame('custom_prefix', StorageFactory::get_apcu_prefix());
+    }
+
+    #[Test]
+    public function get_apcu_prefix_reads_from_option(): void
+    {
+        GlobalFunctionState::$options['wp_prometheus_apcu_prefix'] = 'opt_prefix';
+
+        $this->assertSame('opt_prefix', StorageFactory::get_apcu_prefix());
+    }
+
+    // ── save_config() ────────────────────────────────────────────────
+
+    #[Test]
+    public function save_config_stores_adapter(): void
+    {
+        StorageFactory::save_config(['adapter' => 'redis']);
+
+        $this->assertSame(
+            'redis',
+            GlobalFunctionState::$options['wp_prometheus_storage_adapter']
+        );
+    }
+
+    #[Test]
+    public function save_config_stores_redis_config(): void
+    {
+        StorageFactory::save_config([
+            'redis' => [
+                'host'     => '10.0.0.5',
+                'port'     => 6390,
+                'password' => 'pass123',
+                'database' => 1,
+                'prefix'   => 'TEST_',
+            ],
+        ]);
+
+        $saved = GlobalFunctionState::$options['wp_prometheus_redis_config'];
+        $this->assertSame('10.0.0.5', $saved['host']);
+        $this->assertSame(6390, $saved['port']);
+        $this->assertSame('pass123', $saved['password']);
+        $this->assertSame(1, $saved['database']);
+        // sanitize_key lowercases the prefix
+        $this->assertSame('test_', $saved['prefix']);
+    }
+
+    #[Test]
+    public function save_config_stores_apcu_prefix(): void
+    {
+        StorageFactory::save_config(['apcu_prefix' => 'my_apcu']);
+
+        $this->assertSame(
+            'my_apcu',
+            GlobalFunctionState::$options['wp_prometheus_apcu_prefix']
+        );
+    }
+
+    #[Test]
+    public function save_config_resets_singleton(): void
+    {
+        // Get an adapter (creates singleton).
+        $adapter1 = StorageFactory::get_adapter();
+
+        // Save new config (should reset singleton).
+        StorageFactory::save_config(['adapter' => 'inmemory']);
+
+        // Get adapter again — should be a new instance.
+        $adapter2 = StorageFactory::get_adapter();
+        $this->assertNotSame($adapter1, $adapter2);
+    }
+
+    // ── test_connection() ────────────────────────────────────────────
+
+    #[Test]
+    public function test_connection_inmemory_always_succeeds(): void
+    {
+        $result = StorageFactory::test_connection(StorageFactory::ADAPTER_INMEMORY);
+
+        $this->assertTrue($result['success']);
+        $this->assertNotEmpty($result['message']);
+    }
+
+    #[Test]
+    public function test_connection_unknown_adapter_fails(): void
+    {
+        $result = StorageFactory::test_connection('unknown');
+
+        $this->assertFalse($result['success']);
+        $this->assertStringContainsString('Unknown', $result['message']);
+    }
+
+    #[Test]
+    public function test_connection_redis_fails_without_extension(): void
+    {
+        $extensionLoaded = $this->getFunctionMock(
+            'Magdev\\WpPrometheus\\Metrics',
+            'extension_loaded'
+        );
+        $extensionLoaded->expects($this->any())->willReturn(false);
+
+        $result = StorageFactory::test_connection(StorageFactory::ADAPTER_REDIS);
+        $this->assertFalse($result['success']);
+        $this->assertStringContainsString('not installed', $result['message']);
+    }
+
+    #[Test]
+    public function test_connection_apcu_fails_without_extension(): void
+    {
+        $extensionLoaded = $this->getFunctionMock(
+            'Magdev\\WpPrometheus\\Metrics',
+            'extension_loaded'
+        );
+        $extensionLoaded->expects($this->any())->willReturn(false);
+
+        $result = StorageFactory::test_connection(StorageFactory::ADAPTER_APCU);
+        $this->assertFalse($result['success']);
+        $this->assertStringContainsString('not installed', $result['message']);
+    }
+
+    // ── get_adapter() / reset() / singleton ──────────────────────────
+
+    #[Test]
+    public function get_adapter_returns_inmemory_by_default(): void
+    {
+        $adapter = StorageFactory::get_adapter();
+        $this->assertInstanceOf(InMemory::class, $adapter);
+    }
+
+    #[Test]
+    public function get_adapter_returns_singleton(): void
+    {
+        $adapter1 = StorageFactory::get_adapter();
+        $adapter2 = StorageFactory::get_adapter();
+
+        $this->assertSame($adapter1, $adapter2);
+    }
+
+    #[Test]
+    public function reset_clears_singleton_and_error(): void
+    {
+        StorageFactory::get_adapter();
+        StorageFactory::reset();
+
+        // After reset, get_last_error should be empty.
+        $this->assertEmpty(StorageFactory::get_last_error());
+
+        // Getting adapter again creates a new instance.
+        $adapter = StorageFactory::get_adapter();
+        $this->assertInstanceOf(InMemory::class, $adapter);
+    }
+
+    #[Test]
+    public function get_adapter_falls_back_to_inmemory_when_redis_unavailable(): void
+    {
+        $this->setEnv('WP_PROMETHEUS_STORAGE_ADAPTER', 'redis');
+
+        $extensionLoaded = $this->getFunctionMock(
+            'Magdev\\WpPrometheus\\Metrics',
+            'extension_loaded'
+        );
+        $extensionLoaded->expects($this->any())->willReturn(false);
+
+        $adapter = StorageFactory::get_adapter();
+        $this->assertInstanceOf(InMemory::class, $adapter);
+        $this->assertNotEmpty(StorageFactory::get_last_error());
+    }
+
+    #[Test]
+    public function get_adapter_falls_back_to_inmemory_when_apcu_unavailable(): void
+    {
+        $this->setEnv('WP_PROMETHEUS_STORAGE_ADAPTER', 'apcu');
+
+        $extensionLoaded = $this->getFunctionMock(
+            'Magdev\\WpPrometheus\\Metrics',
+            'extension_loaded'
+        );
+        $extensionLoaded->expects($this->any())->willReturn(false);
+
+        $adapter = StorageFactory::get_adapter();
+        $this->assertInstanceOf(InMemory::class, $adapter);
+        $this->assertNotEmpty(StorageFactory::get_last_error());
+    }
+
+    // ── Helpers ──────────────────────────────────────────────────────
+
+    private function setEnv(string $name, string $value): void
+    {
+        putenv("$name=$value");
+        $this->envVarsToClean[] = $name;
+    }
+}

tests/Unit/TestCase.php

@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Magdev\WpPrometheus\Tests\Unit;
+
+use Magdev\WpPrometheus\Tests\Helpers\GlobalFunctionState;
+use phpmock\phpunit\PHPMock;
+use PHPUnit\Framework\TestCase as PHPUnitTestCase;
+
+/**
+ * Base test case for WP Prometheus unit tests.
+ *
+ * Provides the PHPMock trait for mocking WordPress functions
+ * called from namespaced code, and resets global state between tests.
+ */
+abstract class TestCase extends PHPUnitTestCase
+{
+    use PHPMock;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        GlobalFunctionState::reset();
+    }
+
+    protected function tearDown(): void
+    {
+        GlobalFunctionState::reset();
+        parent::tearDown();
+    }
+}

tests/bootstrap.php

@@ -0,0 +1,450 @@
+<?php
+/**
+ * PHPUnit bootstrap file for WP Prometheus tests.
+ *
+ * Defines WordPress constants and global function stubs required
+ * for loading plugin source files without a WordPress environment.
+ *
+ * @package WP_Prometheus\Tests
+ */
+
+declare(strict_types=1);
+
+use Magdev\WpPrometheus\Tests\Helpers\GlobalFunctionState;
+
+// 1. Load Composer autoloader first (for GlobalFunctionState class).
+require_once dirname(__DIR__) . '/vendor/autoload.php';
+
+// 2. Define WordPress constants required by source files.
+define('ABSPATH', '/tmp/wordpress/');
+define('WP_CONTENT_DIR', '/tmp/wordpress/wp-content');
+define('WP_PROMETHEUS_VERSION', '0.5.0');
+define('WP_PROMETHEUS_FILE', dirname(__DIR__) . '/wp-prometheus.php');
+define('WP_PROMETHEUS_PATH', dirname(__DIR__) . '/');
+define('WP_PROMETHEUS_URL', 'https://example.com/wp-content/plugins/wp-prometheus/');
+define('WP_PROMETHEUS_BASENAME', 'wp-prometheus/wp-prometheus.php');
+
+// 3. Define global WordPress function stubs.
+//    These exist so plugin files can be require'd without fatal errors.
+//    Per-test behavior in namespaced code is controlled via php-mock.
+//    Global-scope tests use GlobalFunctionState for controllable behavior.
+
+// -- Translation functions --
+if (!function_exists('__')) {
+    function __(string $text, string $domain = 'default'): string
+    {
+        return $text;
+    }
+}
+
+if (!function_exists('_e')) {
+    function _e(string $text, string $domain = 'default'): void
+    {
+        echo $text;
+    }
+}
+
+if (!function_exists('esc_html__')) {
+    function esc_html__(string $text, string $domain = 'default'): string
+    {
+        return htmlspecialchars($text, ENT_QUOTES, 'UTF-8');
+    }
+}
+
+if (!function_exists('esc_html_e')) {
+    function esc_html_e(string $text, string $domain = 'default'): void
+    {
+        echo htmlspecialchars($text, ENT_QUOTES, 'UTF-8');
+    }
+}
+
+// -- Escaping functions --
+if (!function_exists('esc_html')) {
+    function esc_html(string $text): string
+    {
+        return htmlspecialchars($text, ENT_QUOTES, 'UTF-8');
+    }
+}
+
+if (!function_exists('esc_attr')) {
+    function esc_attr(string $text): string
+    {
+        return htmlspecialchars($text, ENT_QUOTES, 'UTF-8');
+    }
+}
+
+if (!function_exists('esc_url')) {
+    function esc_url(string $url): string
+    {
+        return filter_var($url, FILTER_SANITIZE_URL) ?: '';
+    }
+}
+
+if (!function_exists('esc_url_raw')) {
+    function esc_url_raw(string $url): string
+    {
+        return filter_var($url, FILTER_SANITIZE_URL) ?: '';
+    }
+}
+
+// -- Sanitization functions --
+if (!function_exists('sanitize_text_field')) {
+    function sanitize_text_field(string $str): string
+    {
+        return trim(strip_tags($str));
+    }
+}
+
+if (!function_exists('sanitize_key')) {
+    function sanitize_key(string $key): string
+    {
+        return preg_replace('/[^a-z0-9_\-]/', '', strtolower($key));
+    }
+}
+
+if (!function_exists('sanitize_file_name')) {
+    function sanitize_file_name(string $name): string
+    {
+        return preg_replace('/[^a-zA-Z0-9_.\-]/', '', $name);
+    }
+}
+
+if (!function_exists('sanitize_html_class')) {
+    function sanitize_html_class(string $class): string
+    {
+        return preg_replace('/[^a-zA-Z0-9_\-]/', '', $class);
+    }
+}
+
+if (!function_exists('absint')) {
+    function absint($value): int
+    {
+        return abs((int) $value);
+    }
+}
+
+if (!function_exists('wp_unslash')) {
+    function wp_unslash($value)
+    {
+        return is_string($value) ? stripslashes($value) : $value;
+    }
+}
+
+// -- WordPress utility functions --
+if (!function_exists('wp_parse_url')) {
+    function wp_parse_url(string $url, int $component = -1)
+    {
+        return parse_url($url, $component);
+    }
+}
+
+if (!function_exists('wp_json_encode')) {
+    function wp_json_encode($data, int $options = 0, int $depth = 512)
+    {
+        return json_encode($data, $options, $depth);
+    }
+}
+
+if (!function_exists('wp_generate_uuid4')) {
+    function wp_generate_uuid4(): string
+    {
+        return sprintf(
+            '%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
+            mt_rand(0, 0xffff), mt_rand(0, 0xffff),
+            mt_rand(0, 0xffff),
+            mt_rand(0, 0x0fff) | 0x4000,
+            mt_rand(0, 0x3fff) | 0x8000,
+            mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff)
+        );
+    }
+}
+
+if (!function_exists('wp_generate_password')) {
+    function wp_generate_password(int $length = 12, bool $special = true): string
+    {
+        return substr(bin2hex(random_bytes($length)), 0, $length);
+    }
+}
+
+if (!function_exists('size_format')) {
+    function size_format(int $bytes, int $decimals = 0): string
+    {
+        $units = ['B', 'KB', 'MB', 'GB', 'TB'];
+        $power = $bytes > 0 ? floor(log($bytes, 1024)) : 0;
+        return number_format($bytes / pow(1024, $power), $decimals) . ' ' . $units[$power];
+    }
+}
+
+if (!function_exists('path_is_absolute')) {
+    function path_is_absolute(string $path): bool
+    {
+        return str_starts_with($path, '/') || (bool) preg_match('#^[a-zA-Z]:\\\\#', $path);
+    }
+}
+
+// -- Hook functions (no-ops) --
+if (!function_exists('add_action')) {
+    function add_action(string $hook, $callback, int $priority = 10, int $accepted_args = 1): bool
+    {
+        return true;
+    }
+}
+
+if (!function_exists('add_filter')) {
+    function add_filter(string $hook, $callback, int $priority = 10, int $accepted_args = 1): bool
+    {
+        return true;
+    }
+}
+
+if (!function_exists('remove_all_filters')) {
+    function remove_all_filters(string $hook, $priority = false): bool
+    {
+        return true;
+    }
+}
+
+if (!function_exists('do_action')) {
+    function do_action(string $hook, ...$args): void
+    {
+    }
+}
+
+if (!function_exists('apply_filters')) {
+    function apply_filters(string $hook, $value, ...$args)
+    {
+        return $value;
+    }
+}
+
+// -- Option functions (controllable via GlobalFunctionState) --
+if (!function_exists('get_option')) {
+    function get_option(string $option, $default = false)
+    {
+        if (array_key_exists($option, GlobalFunctionState::$options)) {
+            return GlobalFunctionState::$options[$option];
+        }
+        return $default;
+    }
+}
+
+if (!function_exists('update_option')) {
+    function update_option(string $option, $value, $autoload = null): bool
+    {
+        GlobalFunctionState::recordCall('update_option', $option, $value);
+        GlobalFunctionState::$options[$option] = $value;
+        return true;
+    }
+}
+
+if (!function_exists('delete_option')) {
+    function delete_option(string $option): bool
+    {
+        GlobalFunctionState::recordCall('delete_option', $option);
+        unset(GlobalFunctionState::$options[$option]);
+        return true;
+    }
+}
+
+if (!function_exists('delete_transient')) {
+    function delete_transient(string $transient): bool
+    {
+        GlobalFunctionState::recordCall('delete_transient', $transient);
+        return true;
+    }
+}
+
+if (!function_exists('flush_rewrite_rules')) {
+    function flush_rewrite_rules(bool $hard = true): void
+    {
+        GlobalFunctionState::recordCall('flush_rewrite_rules');
+    }
+}
+
+// -- URL functions --
+if (!function_exists('home_url')) {
+    function home_url(string $path = ''): string
+    {
+        return 'https://example.com' . $path;
+    }
+}
+
+if (!function_exists('admin_url')) {
+    function admin_url(string $path = ''): string
+    {
+        return 'https://example.com/wp-admin/' . $path;
+    }
+}
+
+// -- Conditional functions (controllable via GlobalFunctionState) --
+if (!function_exists('is_admin')) {
+    function is_admin(): bool
+    {
+        return GlobalFunctionState::$options['__is_admin'] ?? false;
+    }
+}
+
+if (!function_exists('wp_doing_ajax')) {
+    function wp_doing_ajax(): bool
+    {
+        return GlobalFunctionState::$options['__wp_doing_ajax'] ?? false;
+    }
+}
+
+if (!function_exists('wp_doing_cron')) {
+    function wp_doing_cron(): bool
+    {
+        return GlobalFunctionState::$options['__wp_doing_cron'] ?? false;
+    }
+}
+
+if (!function_exists('is_multisite')) {
+    function is_multisite(): bool
+    {
+        return false;
+    }
+}
+
+// -- Plugin functions --
+if (!function_exists('load_plugin_textdomain')) {
+    function load_plugin_textdomain(string $domain, $deprecated = false, string $path = ''): bool
+    {
+        return true;
+    }
+}
+
+if (!function_exists('register_activation_hook')) {
+    function register_activation_hook(string $file, $callback): void
+    {
+    }
+}
+
+if (!function_exists('register_deactivation_hook')) {
+    function register_deactivation_hook(string $file, $callback): void
+    {
+    }
+}
+
+// -- Rewrite functions --
+if (!function_exists('add_rewrite_rule')) {
+    function add_rewrite_rule(string $regex, string $redirect, string $after = 'bottom'): void
+    {
+        GlobalFunctionState::recordCall('add_rewrite_rule', $regex, $redirect, $after);
+    }
+}
+
+if (!function_exists('add_rewrite_tag')) {
+    function add_rewrite_tag(string $tag, string $regex, string $query = ''): void
+    {
+        GlobalFunctionState::recordCall('add_rewrite_tag', $tag, $regex, $query);
+    }
+}
+
+// -- HTTP functions --
+if (!function_exists('status_header')) {
+    function status_header(int $code, string $description = ''): void
+    {
+    }
+}
+
+if (!function_exists('hash_equals')) {
+    // hash_equals is a PHP built-in, but define stub just in case.
+}
+
+if (!function_exists('wp_rand')) {
+    function wp_rand(int $min = 0, int $max = 0): int
+    {
+        return random_int($min, max($min, $max ?: PHP_INT_MAX >> 1));
+    }
+}
+
+if (!function_exists('get_bloginfo')) {
+    function get_bloginfo(string $show = '', bool $filter = true): string
+    {
+        return match ($show) {
+            'version' => '6.7',
+            'language' => 'en-US',
+            'name' => 'Test Site',
+            default => '',
+        };
+    }
+}
+
+if (!function_exists('current_user_can')) {
+    function current_user_can(string $capability, ...$args): bool
+    {
+        return true;
+    }
+}
+
+if (!function_exists('deactivate_plugins')) {
+    function deactivate_plugins($plugins, bool $silent = false, $network_wide = null): void
+    {
+    }
+}
+
+if (!function_exists('wp_die')) {
+    function wp_die($message = '', $title = '', $args = []): void
+    {
+        throw new \RuntimeException((string) $message);
+    }
+}
+
+// -- Plugin global authentication functions (from wp-prometheus.php) --
+// Cannot include wp-prometheus.php directly due to constant definitions
+// and side effects. These mirror the production code for testing.
+
+if (!function_exists('wp_prometheus_get_authorization_header')) {
+    function wp_prometheus_get_authorization_header(): string
+    {
+        if (isset($_SERVER['HTTP_AUTHORIZATION'])) {
+            return sanitize_text_field(wp_unslash($_SERVER['HTTP_AUTHORIZATION']));
+        }
+
+        if (isset($_SERVER['REDIRECT_HTTP_AUTHORIZATION'])) {
+            return sanitize_text_field(wp_unslash($_SERVER['REDIRECT_HTTP_AUTHORIZATION']));
+        }
+
+        if (function_exists('apache_request_headers')) {
+            $headers = apache_request_headers();
+            if (isset($headers['Authorization'])) {
+                return sanitize_text_field($headers['Authorization']);
+            }
+        }
+
+        return '';
+    }
+}
+
+// -- WordPress core class stubs --
+if (!class_exists('WP')) {
+    class WP
+    {
+        public array $query_vars = [];
+    }
+}
+
+if (!function_exists('wp_prometheus_authenticate_request')) {
+    function wp_prometheus_authenticate_request(): bool
+    {
+        $auth_token = get_option('wp_prometheus_auth_token', '');
+
+        // If no token is set, deny access.
+        if (empty($auth_token)) {
+            return false;
+        }
+
+        // Check for Bearer token in Authorization header.
+        $auth_header = wp_prometheus_get_authorization_header();
+        if (!empty($auth_header) && preg_match('/Bearer\s+(.*)$/i', $auth_header, $matches)) {
+            return hash_equals($auth_token, $matches[1]);
+        }
+
+        // Check for token in query parameter.
+        if (isset($_GET['token']) && hash_equals($auth_token, sanitize_text_field(wp_unslash($_GET['token'])))) {
+            return true;
+        }
+
+        return false;
+    }
+}

wp-prometheus.php

@@ -3,7 +3,7 @@
  * Plugin Name: WP Prometheus
  * Plugin URI: https://src.bundespruefstelle.ch/magdev/wp-prometheus
  * Description: Prometheus metrics endpoint for WordPress with extensible hooks for custom metrics.
- * Version: 0.1.1
+ * Version: 0.5.0
  * Requires at least: 6.4
  * Requires PHP: 8.3
  * Author: Marco Graetsch
@@ -21,12 +21,185 @@ if ( ! defined( 'ABSPATH' ) ) {
     exit;
 }
 
+/**
+ * Early metrics request detection.
+ *
+ * Detects /metrics requests early and removes problematic content filters
+ * to prevent recursion issues with Twig-based plugins. Unlike the previous
+ * "early mode", this allows WordPress to continue loading so that third-party
+ * plugins can register their wp_prometheus_collect_metrics hooks.
+ *
+ * Two modes are available:
+ * - Safe mode (default): Removes filters early, lets WP load, fires custom hooks
+ * - Isolated mode: Outputs metrics immediately without custom hooks (legacy early mode)
+ */
+function wp_prometheus_early_metrics_check(): void {
+    // Only handle /metrics requests.
+    $request_uri = isset( $_SERVER['REQUEST_URI'] ) ? sanitize_text_field( wp_unslash( $_SERVER['REQUEST_URI'] ) ) : '';
+    $path        = wp_parse_url( $request_uri, PHP_URL_PATH );
+
+    if ( ! preg_match( '#/metrics/?$#', $path ) ) {
+        return;
+    }
+
+    // Set flag to indicate we're handling a metrics request.
+    define( 'WP_PROMETHEUS_METRICS_REQUEST', true );
+
+    // Check if isolated mode is enabled via environment variable.
+    $env_isolated = getenv( 'WP_PROMETHEUS_ISOLATED_MODE' );
+    $isolated_mode = false !== $env_isolated && in_array( strtolower( $env_isolated ), array( '1', 'true', 'yes', 'on' ), true );
+
+    // Check if isolated mode is enabled via option (legacy "early mode" setting).
+    if ( ! $isolated_mode && ! get_option( 'wp_prometheus_disable_early_mode', false ) ) {
+        // Check for legacy isolated mode option.
+        $isolated_mode = (bool) get_option( 'wp_prometheus_isolated_mode', false );
+    }
+
+    // Remove all content filters immediately to prevent recursion with Twig-based plugins.
+    // This is done for BOTH safe mode and isolated mode.
+    add_action( 'plugins_loaded', 'wp_prometheus_remove_content_filters', 0 );
+
+    // Also remove filters now in case they were added by mu-plugins.
+    wp_prometheus_remove_content_filters();
+
+    // If isolated mode is enabled, handle metrics immediately without waiting for plugins.
+    if ( $isolated_mode ) {
+        wp_prometheus_isolated_metrics_handler();
+    }
+}
+
+/**
+ * Remove content filters that can cause recursion.
+ *
+ * Called early during metrics requests to prevent infinite loops
+ * with Twig-based plugins that hook into content filters.
+ *
+ * @return void
+ */
+function wp_prometheus_remove_content_filters(): void {
+    remove_all_filters( 'the_content' );
+    remove_all_filters( 'the_excerpt' );
+    remove_all_filters( 'get_the_excerpt' );
+    remove_all_filters( 'the_title' );
+    remove_all_filters( 'the_content_feed' );
+    remove_all_filters( 'comment_text' );
+}
+
+/**
+ * Handle metrics in isolated mode (no custom hooks).
+ *
+ * This is the legacy "early mode" that outputs metrics immediately
+ * without allowing third-party plugins to add custom metrics.
+ *
+ * @return void
+ */
+function wp_prometheus_isolated_metrics_handler(): void {
+    // Check if autoloader exists.
+    $autoloader = __DIR__ . '/vendor/autoload.php';
+    if ( ! file_exists( $autoloader ) ) {
+        return;
+    }
+
+    require_once $autoloader;
+
+    // Check license validity.
+    if ( ! \Magdev\WpPrometheus\License\Manager::is_license_valid() ) {
+        return; // Let normal flow handle unlicensed state.
+    }
+
+    // Authenticate using shared helper.
+    if ( ! wp_prometheus_authenticate_request() ) {
+        status_header( 401 );
+        header( 'WWW-Authenticate: Bearer realm="WP Prometheus Metrics"' );
+        header( 'Content-Type: text/plain; charset=utf-8' );
+        echo 'Unauthorized';
+        exit;
+    }
+
+    // Set flag to indicate isolated mode - Collector will skip extensibility hooks.
+    define( 'WP_PROMETHEUS_ISOLATED_MODE', true );
+
+    // Output metrics and exit immediately.
+    $collector = new \Magdev\WpPrometheus\Metrics\Collector();
+
+    status_header( 200 );
+    header( 'Content-Type: text/plain; version=0.0.4; charset=utf-8' );
+    header( 'Cache-Control: no-cache, no-store, must-revalidate' );
+    header( 'Pragma: no-cache' );
+    header( 'Expires: 0' );
+
+    // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- Prometheus format.
+    echo $collector->render();
+    exit;
+}
+
+/**
+ * Authenticate a metrics request using Bearer token or query parameter.
+ *
+ * Shared authentication logic used by both the MetricsEndpoint class
+ * and the isolated mode handler to avoid code duplication.
+ *
+ * @return bool True if authenticated, false otherwise.
+ */
+function wp_prometheus_authenticate_request(): bool {
+    $auth_token = get_option( 'wp_prometheus_auth_token', '' );
+
+    // If no token is set, deny access.
+    if ( empty( $auth_token ) ) {
+        return false;
+    }
+
+    // Check for Bearer token in Authorization header.
+    $auth_header = wp_prometheus_get_authorization_header();
+    if ( ! empty( $auth_header ) && preg_match( '/Bearer\s+(.*)$/i', $auth_header, $matches ) ) {
+        return hash_equals( $auth_token, $matches[1] );
+    }
+
+    // Check for token in query parameter (less secure but useful for testing).
+    // phpcs:ignore WordPress.Security.NonceVerification.Recommended -- Auth token check.
+    if ( isset( $_GET['token'] ) && hash_equals( $auth_token, sanitize_text_field( wp_unslash( $_GET['token'] ) ) ) ) {
+        return true;
+    }
+
+    return false;
+}
+
+/**
+ * Get the Authorization header from the request.
+ *
+ * Checks multiple sources for the Authorization header to support
+ * different server configurations (Apache, nginx, CGI, etc.).
+ *
+ * @return string The Authorization header value, or empty string if not found.
+ */
+function wp_prometheus_get_authorization_header(): string {
+    if ( isset( $_SERVER['HTTP_AUTHORIZATION'] ) ) {
+        return sanitize_text_field( wp_unslash( $_SERVER['HTTP_AUTHORIZATION'] ) );
+    }
+
+    if ( isset( $_SERVER['REDIRECT_HTTP_AUTHORIZATION'] ) ) {
+        return sanitize_text_field( wp_unslash( $_SERVER['REDIRECT_HTTP_AUTHORIZATION'] ) );
+    }
+
+    if ( function_exists( 'apache_request_headers' ) ) {
+        $headers = apache_request_headers();
+        if ( isset( $headers['Authorization'] ) ) {
+            return sanitize_text_field( $headers['Authorization'] );
+        }
+    }
+
+    return '';
+}
+
+// Try early metrics handling before full plugin initialization.
+wp_prometheus_early_metrics_check();
+
 /**
  * Plugin version.
  *
  * @var string
  */
-define( 'WP_PROMETHEUS_VERSION', '0.1.1' );
+define( 'WP_PROMETHEUS_VERSION', '0.5.0' );
 
 /**
  * Plugin file path.