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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.

Tonya Mork

This WordPress plugin is a wrapper for the <a href="https://kint-php.github.io/kint/" rel="nofollow ugc">Kint</a> PHP Debugger utility version 1.x. Now instead of using var_dump() or print_r(), you simply use d() with zero, nadda, no formatting required.
Use this tool when you are debugging your website, in place of <a href="http://php.net/manual/en/function.var-dump.php" rel="nofollow ugc">var_dump()</a>, <a href="http://php.net/manual/en/function.print-r.php" rel="nofollow ugc">print_r()</a> and <a href="http://php.net/manual/en/function.debug-backtrace.php" rel="nofollow ugc">debug_backtrace()</a>.
<h4>Handy Tools</h4>
Some handy tools just for the PHP Developer:
<ul>
<li><code>d( $var );</code> to render a collapsible UI container which displays your variable data in “the most informative way”</li>
<li><code>ddd( $var );</code> same as d() except that it also executes <code>die()</code> to halt execution.</li>
</ul>
Here are some variations of <code>d()</code> to give you the display you want:
<ul>
<li><code>~d( $var );</code> outputs in plain text format.</li>
<li><code>+d( $var );</code> disregards depth level limits and outputs everything</li>
<li><code>!d( $var );</code> shows expanded rich output</li>
<li><code>-d( $var );</code> attempts to ob_clean() the previous output (dump something inside of HTML)</li>
</ul>
<h4>Profiler</h4>
Kint even includes a naïve profiler, which can help you analyze which blocks of code take longer than others:
<pre><code>Kint::dump( microtime() ); // just pass microtime()
sleep( 1 );
Kint::dump( microtime(), 'after sleep(1)' );
sleep( 2 );
ddd( microtime(), 'final call, after sleep(2)' );
</code></pre>
See <a href="https://wordpress.org/extend/plugins/kint-php-debugger/screenshots/" rel="ugc">screenshot 2</a> for what is rendered out in your browser.
<h3>Admin Bar</h3>
“KINT ACTIVE” indicator displays in the WordPress admin bar to alert you when the plugin is active.

Kint PHP Debugger

Really like to debug with Kint, and this plugin makes it much easier.



Useful

Love this plugin. Displays more than var_dump does and is so much easier to read the output. Handy toggle to display more information is very helpful. Love that ddd() option to display and stop execution. Thank you!!!



Improves Workflow and Troubleshooting

Thanks for this plugin. It makes debugging my arrays of arrays of arrays much simpler. ;)

Works great!

Saves a lot of time when writing plugins and themes.
Thanks!

Update 2/11/2021 - even though this plugin hasn't had any updated in more than 2 years, it is still working just great.

Does what it says

Kint is a modern and powerful PHP debugging helper, which requires zero-setup and replaces var_dump(), print_r() and debug_backtrace().

CU Debug Tool by CodeUnion vs Kint PHP Debugger