JQuery Monitor – what it can do for you!

https://wordpress.org/plugins/query-monitor/

Description
Query Monitor is the developer tools panel for WordPress. It enables debugging of database queries, PHP errors, hooks and actions, block editor blocks, enqueued scripts and stylesheets, HTTP API calls, and more.

It includes some advanced features such as debugging of Ajax calls, REST API calls, and user capability checks. It includes the ability to narrow down much of its output by plugin or theme, allowing you to quickly determine poorly performing plugins, themes, or functions.

Query Monitor focuses heavily on presenting its information in a useful manner, for example by showing aggregate database queries grouped by the plugins, themes, or functions that are responsible for them. It adds an admin toolbar menu showing an overview of the current page, with complete debugging information shown in panels once you select a menu item.

For complete information, please see the Query Monitor website.

Here’s an overview of what’s shown for each page load:

Database queries, including notifications for slow, duplicate, or erroneous queries. Allows filtering by query type (SELECT, UPDATE, DELETE, etc), responsible component (plugin, theme, WordPress core), and calling function, and provides separate aggregate views for each.
The template filename, the complete template hierarchy, and names of all template parts that were loaded or not loaded.
PHP errors presented nicely along with their responsible component and call stack, and a visible warning in the admin toolbar.
Blocks and associated properties in post content when using WordPress 5.0+ or the Gutenberg plugin.
Matched rewrite rules, associated query strings, and query vars.
Enqueued scripts and stylesheets, along with their dependencies, dependents, and alerts for broken dependencies.
Language settings and loaded translation files (MO files) for each text domain.
HTTP API requests, with response code, responsible component, and time taken, with alerts for failed or erroneous requests.
User capability checks, along with the result and any parameters passed to the capability check.
Environment information, including detailed information about PHP, the database, WordPress, and the web server.
The values of all WordPress conditional functions such as is_single(), is_home(), etc.
Transients that were updated.
In addition:

Whenever a redirect occurs, Query Monitor adds an HTTP header containing the call stack, so you can use your favourite HTTP inspector or browser developer tools to trace what triggered the redirect.
The response from any jQuery-initiated Ajax request on the page will contain various debugging information in its headers. PHP errors also get output to the browser’s developer console.
The response from an authenticated WordPress REST API request will contain various debugging information in its headers, as long as the authenticated user has permission to view Query Monitor’s output.
By default, Query Monitor’s output is only shown to Administrators on single-site installations, and Super Admins on Multisite installations.

In addition to this, you can set an authentication cookie which allows you to view Query Monitor output when you’re not logged in (or if you’re logged in as a non-Administrator). See the Settings panel for details.

PRIVACY STATEMENT
Query Monitor is private by default and always will be. It does not persistently store any of the data that it collects. It does not send data to any third party, nor does it include any third party resources.

Query Monitor’s full privacy statement can be found here.

https://github.com/johnbillion/query-monitor#features

The Developer Tools Panel for WordPress

https://querymonitor.com

Files

Query Monitor is the developer tools panel for WordPress. It enables debugging of database queries, PHP errors, hooks and actions, block editor blocks, enqueued scripts and stylesheets, HTTP API calls, and more.

It includes some advanced features such as debugging of Ajax calls, REST API calls, and user capability checks. It includes the ability to narrow down much of its output by plugin or theme, allowing you to quickly determine poorly performing plugins, themes, or functions.

Query Monitor focuses heavily on presenting its information in a useful manner, for example by showing aggregate database queries grouped by the plugins, themes, or functions that are responsible for them. It adds an admin toolbar menu showing an overview of the current page, with complete debugging information shown in panels once you select a menu item.

Here’s an example of Query Monitor’s output. This is the panel showing aggregate database queries grouped by component:

• Features
  • Database Queries
  • Hooks
  • Theme
  • PHP Errors
  • Request
  • Scripts & Styles
  • Languages
  • HTTP API Requests
  • Redirects
  • Ajax
  • REST API
  • Admin Screen
  • Environment Information
  • Logging
  • Profiling
  • Everything Else
• Notes
  • Implementation
• Screenshots
• FAQ
• Privacy Statement
• Related Tools
• Contributing
• Icon
• License

Features

Database Queries

• Shows all database queries performed on the current request
• Shows affected rows and time for all queries
• Shows notifications for slow queries, duplicate queries, and queries with errors
• Filter queries by query type (SELECT, UPDATE, DELETE, etc)
• Filter queries by component (WordPress core, Plugin X, Plugin Y, theme)
• Filter queries by calling function
• View aggregate query information grouped by component, calling function, and type
• Super advanced: Supports multiple instances of wpdb (more info in the FAQ)

Filtering queries by component or calling function makes it easy to see which plugins, themes, or functions on your site are making the most (or the slowest) database queries.

Hooks

• Shows all hooks fired on the current request, along with hooked actions, their priorities, and their components
• Filter hooks by part of their name
• Filter actions by component (WordPress core, Plugin X, Plugin Y, theme)

Theme

• Shows the template filename for the current request
• Shows the complete template hierarchy for the current request (WordPress 4.7+)
• Shows all template parts loaded or not loaded on the current request
• Shows the available body classes for the current request
• Shows the active theme name

PHP Errors

• PHP errors (warnings, notices, stricts, and deprecated) are presented nicely along with their component and call stack
• Shows an easily visible warning in the admin toolbar

do_action( 'qm/debug', 'This happened!' );

do_action( 'qm/warning', 'Unexpected value of {foo} encountered', [
    'foo' => $foo,
] );

if ( is_wp_error( $response ) ) {
    do_action( 'qm/error', $response );
}

try {
    // your code
} catch ( Exception $e ) {
    do_action( 'qm/error', $e );
}

QM::error( 'Everything is broken' );

// Start the 'foo' timer:
do_action( 'qm/start', 'foo' );

// Run some code
my_potentially_slow_function();

// Stop the 'foo' timer:
do_action( 'qm/stop', 'foo' );

// Start the 'bar' timer:
do_action( 'qm/start', 'bar' );

// Iterate over some data:
foreach ( range( 1, 10 ) as $i ) {
    my_potentially_slow_function( $i );
    do_action( 'qm/lap', 'bar' );
}

// Stop the 'bar' timer:
do_action( 'qm/stop', 'bar' );

If your WP_CONTENT_DIR isn’t writable and therefore the symlink for db.php can’t be put in place, Query Monitor still functions, but this extended functionality won’t be available. You can manually create the db.php symlink if you have permission.

Screenshots

Admin Toolbar Menu

Database Queries

Capability Checks

Aggregate Database Queries by Component

Aggregate Database Queries by Calling Function

Hooks and Actions

HTTP API Requests

Frequently Asked Questions

Who can see Query Monitor’s output?

By default, Query Monitor’s output is only shown to Administrators on single-site installations, and Super Admins on Multisite installations.

In addition to this, you can set an authentication cookie which allows you to view Query Monitor output when you’re not logged in (or if you’re logged in as a non-administrator). See the Settings panel for details.

Does Query Monitor itself impact the page generation time or memory usage?

Short answer: Yes, but only a little.

Long answer: Query Monitor has a small impact on page generation time because it hooks into a few places in WordPress in the same way that other plugins do. The impact is negligible.

On pages that have an especially high number of database queries (in the hundreds), Query Monitor currently uses more memory than I would like it to. This is due to the amount of data that is captured in the stack trace for each query. I have been and will be working to continually reduce this.

Are there any add-on plugins for Query Monitor?

A list of add-on plugins for Query Monitor can be found here.

In addition, Query Monitor transparently supports add-ons for the Debug Bar plugin. If you have any Debug Bar add-ons installed, just deactivate Debug Bar and the add-ons will show up in Query Monitor’s menu.

Where can I suggest a new feature or report a bug?

Please use the issue tracker on Query Monitor’s GitHub repo as it’s easier to keep track of issues there, rather than on the wordpress.org support forums.

Is Query Monitor available on WordPress.com VIP Go?

Yep! However, a user needs to be granted the view_query_monitor capability to see Query Monitor even if they’re an administrator.

I’m using multiple instances of wpdb. How do I get my additional instances to show up in Query Monitor?

You’ll need to hook into the qm/collect/db_objects filter and add an item to the array containing your wpdb instance. For example:

add_filter( 'qm/collect/db_objects', function( $objects ) {
	$objects['my_db'] = $GLOBALS['my_db'];
	return $objects;
} );

Your wpdb instance will then show up as a separate panel, and the query time and query count will show up separately in the admin toolbar menu. Aggregate information (queries by caller and component) will not be separated.

Can I click on stack traces to open the file in my editor?

Yes! You can enable this on the Settings panel.

Do you accept donations?

No, I do not accept donations. If you like the plugin, I’d love for you to leave a review. Tell all your friends about the plugin too!

Privacy Statement

Query Monitor is private by default and always will be. It does not persistently store any of the data that it collects. It does not send data to any third party, nor does it include any third party resources.

Query Monitor’s full privacy statement can be found here.

Related Tools

Debugging is rarely done with just one tool. Along with Query Monitor, you should be aware of other plugins and tools which aid in debugging and profiling your website. Here are some examples:

• Tideways or XHProf for low level profiling of PHP.
• Xdebug for a host of PHP debugging tools.
• P3 Profiler for performance trend analysis of the plugins in use on your site.
• Time Stack for WordPress-specific operation profiling.
• Laps for lightweight WordPress profiling.
• Clockwork for debugging and profiling PHP applications.
• Blackfire for PHP performance testing.
• New Relic for complete software performance analytics.

Query Monitor also has several add-on plugins which extend its functionality, and transparently supports add-ons for the Debug Bar plugin (see the FAQ for more info).

See also my list of WordPress Developer Plugins.

Contributing

Code contributions, feedback, and feature suggestions are very welcome. See CONTRIBUTING.md for more details.

Icon

Query Monitor’s icon was designed by Tubagus Didin Asrori.

License: GPLv2

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.