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.

Matthew Batchelder

vhauri

This plugin is basically a wrapper for the excellent dBug (http://dbug.ospinto.com) class for PHP debugging, written by Kwaku Otchere..
Instead of var_dump or echo, you can call wp_dbug( $variable ) to get clear, dynamic debug output of strings, arrays, or objects.
Thanks to @borkweb, the plugin is now compatible with the WP Debug Bar plugin (https://wordpress.org/extend/plugins/debug-bar/) for extra debugging goodness!

wp-dBug

Plugin implements the awesome dBug class created by Kwaku Otchere for use in WordPress plugin debugging

CU Debug Tool by CodeUnion vs wp-dBug