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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.

Silkalns

WP Chill

Brian Fegter

Chris Dillon

Razvan Aldea

For admins, developers, and support staff, Debug This provides a ton of information about your WordPress installation, all from the front-end admin bar.
<ul>
<li>The current WP_Query object</li>
<li>Blog info and options</li>
<li>Embed providers</li>
<li>Files in rendered HTML (CSS, images, JavaScript)</li>
<li>Filters and actions</li>
<li>Images sizes</li>
<li>Globals and constants</li>
<li>Menus</li>
<li>Object cache stats</li>
<li>Plugins, must-use plugins, and dropins</li>
<li>Rewrite rules</li>
<li>Queries</li>
<li>PHP and server information</li>
<li>Post attachments</li>
<li>Post types</li>
<li>Scripts and styles enqueued</li>
<li>Shortcodes</li>
<li>Sidebars and widgets</li>
<li>Taxonomies and terms</li>
<li>Themes</li>
<li>Users</li>
<li>WP cron schedules and jobs</li>
<li>WP debug log</li>
</ul>
Debug This helps you save time and effort when trying to figure out what’s going on. Instead of hardcoding debug snippets or writing complex unit 
tests for small functionality, you can simply bring to the surface what you need right from the admin bar.
For example, when viewing a single post, you can see:
<ul>
<li>a list of post attachments,</li>
<li>which menus and sidebars are being displayed,</li>
<li>the post type, post fields, and meta data,</li>
<li>the current query variables and query string,</li>
<li>the rewrite rules applied,</li>
<li>the author,</li>
<li>the terms,</li>
<li>and much more.</li>
</ul>
<h3>Extend</h3>
<h4>Debug This Functions</h4>
New debug modes can be created easily:
<pre><code>add_debug_extension(
 $mode,
 $menu_label,
 $description,
 $callback,
 $group = 'General'
);
</code></pre>
Example
<pre><code>add_debug_extension(
 'actions',
 __('Actions', 'debug-this'),
 __('$wp_actions contains all active registered actions', 'debug-this'),
 'foo_callback',
 'Filters And Actions'
);
function foo_callback($buffer, $template){
 global $wp_actions;
 $debug = print_r($wp_actions, true);
 return $debug;
}
</code></pre>
You can add links to the header of a debug mode page. Place this code within your debug callback function.
<pre><code>add_debug_header_link('http://urltolink', 'Link Label');
</code></pre>
Extensions can be removed as well using <code>remove_debug_extension($mode);</code>
No PRE Tags
If you don’t want your debug output to be enclosed in PRE tags, simply set the following in your extension:
<pre><code>Debug_This::$no_pre = true;
</code></pre>
Saved Queries and Execution Time
Retrieve saved queries and execution time by using the following static properties:
<ul>
<li><code>Debug_This::$execution_time</code></li>
<li><code>Debug_This::$queries</code> – SAVEQUERIES must defined as true</li>
</ul>
URL Helpers
<ul>
<li><code>Debug_This::get_current_debug_url()</code> – current URL with the debug query</li>
<li><code>Debug_This::get_escape_url()</code> – used for the debug escape link that links to original page URL</li>
</ul>
<h4>WP Actions</h4>
<ul>
<li><code>debug_this</code> – receives the $mode arg – outputs the debug code sent from the extension modes. The default action is set to priority 5. This allows you to prepend or append any output without conflict using less or greater priorities.</li>
</ul>
<h4>WP Filters</h4>
There are a few filters you can use to customize Debug This to your needs:
<ul>
<li><code>debug_this_template</code> – receives $template arg – Use your own template</li>
<li><code>debug_this_default_mode</code> – receives $mode arg – Alters the mode for the parent DT admin bar button link.</li>
<li><code>debug_this_output</code> – receives $output, $mode args – Filter debug content before it’s rendered</li>
</ul>
<h4>JavaScript</h4>
To access the built-in Debug This JS functionality, enqueue your custom script with the dependency set to <code>debug-this</code>. Your script will inherit a jQuery dependency.
Object: debugThis
<ul>
<li><code>debugThis.mode</code> – current mode</li>
<li><code>debugThis.defaultMode</code></li>
<li><code>debugThis.template</code> – current included template</li>
<li><code>debugThis.queryVar</code> – the defined query string variable</li>
</ul>
Functions:
<ul>
<li><code>isDebug()</code></li>
<li><code>getDebugMode()</code> – uses <code>isDebug()</code></li>
</ul>
Events:
A jQuery <code>debug-this</code> event is fired from the footer. You can hook into this event with the following;
<pre><code>jQuery(document).bind('debug-this', function(event, debugThis){
 console.log(debugThis);
});
</code></pre>
<h4>Helper Functions</h4>
There are three included functions to help you work with files.
<ul>
<li><code>debug_this_get_file_ownership($file)</code> – returns <code>array('name' => $name, 'group' => $group)</code></li>
<li><code>debug_this_get_file_perms($file)</code> – returns string – Example: 0775</li>
<li><code>debug_this_convert_perms_to_rwx($perms)</code> – returns string – converts permission number to RWX format – Example: 0755 folder becomes drwxr-xr-x</li>
</ul>

Debug This

Very nice, even the phpinfo() colors are displayed correctly.

Great plugin

Peek under the hood with sixty debugging reports just one click away.

CU Debug Tool by CodeUnion vs Debug This