hydr4x

CU Debug Tool is a lightweight yet powerful debugging assistant designed for WordPress developers. Built with a modular architecture, it provides a clean, dark-mode overlay that helps you analyze what is happening under the hood of your WordPress site.
Key Features:
<ul>
<li>Dumps: Tired of cluttering your frontend with <code>var_dump</code> or <code>print_r</code> breaking the layout? Use our helper function <code>cu_dump()</code> to capture variable data cleanly and display it inside the debug panel without affecting your site’s design.</li>
<li>Log Viewer: Don’t want to log in to your server via FTP just to check errors? View the realtime contents of your <code>debug.log</code> file and clear it instantly directly from the toolbar.</li>
<li>ACF Fields Viewer: Working with ACF Blocks or Options pages? Stop guessing the array structure. Instantly inspect clean, readable data for current Post Meta, Global Options, and specific Gutenberg Blocks without the internal metadata noise.</li>
<li>Hooks: Debugging the event-driven architecture? Search for any Action or Filter hook to see a list of all attached callbacks, their priorities, and exactly where they are defined in the code.</li>
<li>Rewrites: Permalink headaches? Test any URL against your active rewrite rules to see exactly which rule matches, what query variables are parsed, and why you might be getting 404 errors.</li>
<li>Globals: Wondering which template is rendering the current page? Need to check active PHP variables, memory usage, or <code>wp-config.php</code> constants? This tab gives you a complete snapshot of the current environment.</li>
<li>Inspector: Your central search engine for WordPress internals. Quickly inspect the raw value of any database Option (<code>get_option</code>) or interactively test specific hooks and rewrites without writing temporary code.</li>
<li>Registry: A comprehensive manifest of your system. View all scheduled WP-Cron events (including overdue status) and use the “Shortcode Detective” to find the exact file and line number where a shortcode is defined.</li>
<li>Assets: Wondering what scripts and styles are loading on the current page? Get a quick, organized list of all enqueued CSS and JavaScript files to debug dependencies.</li>
<li>Mails: Need to verify if WordPress is actually sending emails? Inspect the headers and content of every email sent via <code>wp_mail()</code> during the current request.</li>
<li>SQL Monitor: Analyze database queries on demand. Toggle recording only when you need it to inspect raw SQL, identify slow queries, and spot duplicates without slowing down your site permanently.</li>
<li>Tools: A suite of one-click utilities for developers. Flush rewrite rules, clear Transients (cache), and send test emails to verify SMTP configuration instantly.</li>
</ul>
Security & Performance 
The tool is only visible to administrators (<code>manage_options</code> capability).

CU Debug Tool by CodeUnion

A professional, modular debugging toolbar for developers. Inspect SQL, Rewrite Rules, Hooks, Cron events, and Options without cluttering the frontend.

Forge12 Interactive GmbH

F12 Profiler analyzes your WordPress site comprehensively and delivers concrete, prioritized recommendations to improve load times. The plugin combines server diagnostics, asset analysis, database optimization, and plugin impact assessment in a modern, clean interface.
<h4>Features</h4>
Analysis & Diagnostics
<ul>
<li>Server analysis (PHP, MySQL, OPcache, web server, SSL, HTTP/2, compression)</li>
<li>Automatic site crawler with load time measurement (desktop & mobile)</li>
<li>Asset analysis (CSS, JS, images) with optimization potential</li>
<li>OPcache status & configuration recommendations</li>
<li>PHP profiler (runtime, queries, hooks, plugin ranking, culprit analysis)</li>
<li>Plugin impact analysis (assets, hooks, queries per plugin)</li>
<li>PageSpeed Insights integration (Lighthouse Scores + Core Web Vitals + CrUX)</li>
<li>Performance score with 6 weighted categories (A-F grades, trend delta)</li>
<li>Recommendation engine with automatic optimization suggestions</li>
</ul>
Optimization Tools
<ul>
<li>Lazy Loading (images and iframes)</li>
<li>Font Display Optimization (font-display: swap/optional/fallback/block)</li>
<li>Script Defer Manager (automatic defer for scripts with exclusion list)</li>
<li>Auto Image Dimensions (prevents Layout Shifts / CLS)</li>
<li>HTML Minification (whitespace, comments, empty attributes)</li>
<li>CSS/JS Minification (file-based cache)</li>
<li>WordPress Bloat Removal (emojis, embeds, Dashicons, jQuery Migrate, XML-RPC, Heartbeat, and more)</li>
<li>Browser Cache (.htaccess-based)</li>
<li>DNS Prefetch & Preconnect (domain detection from asset scan)</li>
<li>Database Analysis (8 categories with detail view)</li>
<li>Autoload Manager (granular wp_options management)</li>
<li>Background Asset Scanner with conflict detection</li>
<li>File-based Page Cache with TTL and URL exclusion (Pro)</li>
<li>CSS/JS Asset Manager – disable, defer, async per page or globally (Pro)</li>
<li>Conditional Loading – shortcode, block, regex, archive, login status, post type, plugin (Pro)</li>
<li>Smart auto-suggestions with source-based plugin detection after full scan (Pro)</li>
<li>Asset Preload Manager – Link headers for critical assets (Pro)</li>
<li>Critical CSS Generator & Applier – above-the-fold CSS per template (Pro)</li>
<li>Unused CSS Removal – per page template, safelist, regex safelist (Pro)</li>
<li>WebP Image Conversion with batch queue and backup (Pro)</li>
<li>LQIP Image Placeholders – 20px blur-up previews with IntersectionObserver (Pro)</li>
<li>Preload Key Requests – LCP images, fonts, critical resources (Pro)</li>
<li>Script Delay – delays third-party JS until first user interaction (Pro)</li>
<li>Local Google Fonts – GDPR-compliant WOFF2 self-hosting (Pro)</li>
<li>YouTube/Vimeo Facade – thumbnail + play button instead of iframe (Pro)</li>
<li>Database Cleanup – one-click per category or bulk action (Pro)</li>
<li>Redis Object Cache Management – drop-in installation/removal (Pro)</li>
<li>Scheduled Crawls & Cleanups via WP-Cron (Pro)</li>
<li>Performance Budgets with email/webhook notifications (Pro)</li>
<li>Settings Import/Export as JSON (Pro)</li>
<li>One-Click Optimizer – automated optimization with backup & restore (Pro)</li>
<li>License Management with activation/deactivation (Pro)</li>
</ul>
User Interface
<ul>
<li>Modern iOS-style design system</li>
<li>React 18 + TypeScript SPA</li>
<li>30+ pages/tools with dedicated configuration</li>
<li>Context-sensitive info sections on all pages</li>
<li>Pro features visible with lock icon and upgrade prompt</li>
</ul>
<a href="https://www.forge12.com/f12-profiler-pro/" rel="nofollow ugc">Get F12 Profiler Pro</a>
<h4>System Requirements</h4>
<ul>
<li>WordPress 6.0 or higher</li>
<li>PHP 8.0 or higher</li>
<li>MySQL 5.7 / MariaDB 10.3 or higher</li>
</ul>

F12 Profiler

Excellent! After P3 doesn’t work with PHP7+ anymore, F12 seems finally the one stepping in to fill that gap.

Update [18-Jun-19]. After some small contributions of mine to the dev efforts, the plugin developer has decided to add me to the team, long after this review was written.

Finally an alternative to P3

Comprehensive WordPress performance analysis with crawling, load time measurement, server diagnostics, and integrated optimization tools. Free.

CU Debug Tool by CodeUnion vs F12 Profiler