Query Monitor


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, user capability checks, and full support for block themes and full site editing. 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 (for block themes and classic themes).
  • PHP errors presented nicely along with their responsible component and call stack, and a visible warning in the admin toolbar.
  • Blocks and associated properties within post content and within full site editing (FSE).
  • 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 and JSON 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 an overview of performance information and PHP errors in its headers, as long as the authenticated user has permission to view Query Monitor’s output. An an enveloped REST API request will include even more debugging information in the qm property of the response.

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.

Other Plugins

I maintain several other plugins for developers. Check them out:

  • User Switching provides instant switching between user accounts in WordPress.
  • WP Crontrol lets you view and control what’s happening in the WP-Cron system

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.

Accessibility Statement

Query Monitor aims to be fully accessible to all of its users. It implements best practices for web accessibility, outputs semantic and structured markup, uses the accessibility APIs provided by WordPress and web browsers where appropriate, and is fully accessible via keyboard.

That said, Query Monitor does not conform to the Web Content Accessibility Guidelines (WCAG) 2.0 at level AA like WordPress itself does. The main issue is that the user interface uses small font sizes to maintain a high information density for sighted users. Users with poor vision or poor motor skills may struggle to view or interact with some areas of Query Monitor because of this. This is something which I’m acutely aware of and which I work to gradually improve, but the underlying issue of small font sizes remains.

If you’ve experienced or identified another accessibility issue in Query Monitor, please open a thread in the Query Monitor plugin support forum and I’ll try my best to address it swiftly.


  • Admin Toolbar Menu
  • Aggregate Database Queries by Component
  • Capability Checks
  • Database Queries
  • Hooks and Actions
  • HTTP API Requests
  • Aggregate Database Queries by Calling Function


Does this plugin work with PHP 8?

Yes, it’s actively tested and working up to PHP 8.2.

Who can access 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 when you’re logged in as a user who cannot usually see Query Monitor’s output. 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 WordPress in the same way that other plugins do. The impact is low; typically between 10ms and 100ms depending on the complexity of your site.

Query Monitor’s memory usage typically accounts for around 10% of the total memory used to generate the page.

Can I prevent Query Monitor from collecting data during long-running requests?

Yes, if anything calls do_action( 'qm/cease' ) then Query Monitor will cease operating for the remainder of the page generation. It detaches itself from further data collection, discards any data it’s collected so far, and skips the output of its information.

This is useful for long-running operations that perform a very high number of database queries, consume a lot of memory, or otherwise are of no concern to Query Monitor, for example:

  • Backing up or restoring your site
  • Exporting a large amount of data
  • Running security scans

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, 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 Altis?

Yes, the Altis Developer Tools are built on top of Query Monitor.

Is Query Monitor available on WordPress.com VIP?

Yes, but a user needs to be granted the view_query_monitor capability to see Query Monitor even if they’re an administrator. See the WordPress.com VIP documentation for more details.

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

This feature was removed in version 3.12 as it was rarely used and considerably increased the maintenance burden of Query Monitor itself. Feel free to continue using version 3.11 if you need to make use of this feature.

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?

I am accepting sponsorships via the GitHub Sponsors program. If you work at an agency that develops with WordPress, ask your company to provide sponsorship in order to invest in its supply chain. The tools that I maintain probably save your company time and money, and GitHub sponsorship can now be done at the organisation level.

In addition, if you like the plugin then I’d love for you to leave a review. Tell all your friends about it too!


July 4, 2023
Tenia un problema de carga en el wordpress y consegui sacar el error en menos de 5 minutos
July 1, 2023 1 reply
...it would be nice to have an option to deactivate the plugin on mobile devices. I noticed that it slows down the loading and time to be able to interact with the pages significantly. Sure, sometimes it would be useful to have it on mobile as well, and that could be added as an option.Otherwise it's a great, no the best plugin for that use case 😀👍
May 23, 2023
I discovered the "Set authentication cookie" today (which solved a problem I had in a really smart way). Thank you, everything about this plugin makes me happy (UI, Code, Concepts, Update-Frequency, Reliability, ...)
May 12, 2023
Its user-friendly interface and compatibility with other plugins and tools make it a great addition to any developer's toolkit. I highly recommend it to anyone looking to improve their WordPress site's performance.
April 15, 2023
If this plugin would not exist one would have to program it immediately! Helps in development, debugging, optimization, and much more.
Read all 422 reviews

Contributors & Developers

“Query Monitor” is open source software. The following people have contributed to this plugin.


“Query Monitor” has been translated into 20 locales. Thank you to the translators for their contributions.

Translate “Query Monitor” into your language.

Interested in development?

Browse the code, check out the SVN repository, or subscribe to the development log by RSS.



  • Improves theme template part data collection when the Gutenberg plugin is in use with a block theme
  • Skips attempting to resolve a block template if the theme doesn’t support block templates
  • Removes the fallback to $EZSQL_ERROR for database query errors as it’s not possible to determine if the error should be ignored


  • Adds the total count to the table footer of the PHP Errors panel
  • Improves the destination URL for links that point to the site editor
  • Implements some minor visual improvements
  • Removes unreliable information about the transport for HTTP API requests
  • Removes Query Monitor output from the interim login modal


  • Corrects some inter-panel links that point to the Queries panel and sub-panels
  • Switches to sessionStorage for the selected table column filters so they don’t persist across tabs or sessions
  • Removes the “Debug Bar:” prefix on the menus for panels inherited from the Debug Bar plugin


  • Clarifies and improves information in the Template panel when a block theme or full site editing (FSE) is in use
  • Avoids PHP warnings if a third party plugin makes unexpected changes to language file paths
  • Implements some minor performance improvements
  • Removes misleading information about WordPress memory limits
  • Removes support for multiple instances of wpdb (see the FAQ for more information)


  • Implements various accessibility improvements
  • Fixes an issue where not all admin area footer scripts were shown in the Scripts panel
  • Improves output when the SQLite feature in the Performance Labs plugin is in use
  • Removes QM output altogether from the Customizer
  • Ensures wp-content/db.php from another plugin doesn’t get removed when deactivating QM


  • Avoids a fatal error in PHP 8 when posix_getpwuid() or posix_getgrgid() doesn’t return an expected value.


  • Adds a new “Multisite” panel that shows usage of switch_to_blog() and restore_current_blog() on Multisite installations
  • Improves the output shown for blocks and template parts when block themes or full site editing is in use
  • Introduces new QM_Data and QM_Component classes to make the data collection more structured and reliable
  • Increases the minimum supported version of PHP to 7.2
  • Improves the performance of SVG icons
  • Removes the ability to completely hide silenced PHP errors
  • Avoids some deprecated notices in PHP 8.2
  • Improves the performance of the PHP class autoloader


  • Prevents logging duplicate entries for multiple calls to load the same translation file
  • Brings the dispatcher priority back down to 9 for maximum compatibility with other plugins that use a shutdown handler


  • Adds information about the current language on the Languages panel
  • Reduces the chance that Query Monitor blames itself for PHP errors that don’t have a stack trace
  • Replaces the use of Dashicons with inline SVGs and removes the dashicons dependency
  • Switches to class autoloading via Composer for reduced memory usage
  • Changes the priority of the shutdown dispatcher from 0 to PHP_INT_MAX to ensure as much data as possible is collected
  • Improves the styling of Debug Bar add-ons
  • Fixes some erroneous localisation of float values in REST API output
  • Bumps the minimum supported PHP version to 5.6
  • Improves various other bits and bobs


  • Introduces a dark mode toggle on the Settings panel, which replaces the QM_DARK_MODE constant
  • Prevents errors with undefined constants being reported in db.php
  • Adds more comprehensive handling of unexpected values in stack traces
  • Fixes PHP Warning ‘Header may not contain NUL bytes’ when outputting headers


  • Fixes some deprecated notices with PHP 8.1
  • Improves the handling of SQL queries that consist only of MySQL comments


  • Fixes an incompatibility with PHP versions prior to 7.2
  • Fixes a warning that was being triggered within the PHP header dispatcher
  • Introduces the qm/component_type/{$type} filter
  • Introduces a QM_VERSION constant


  • Introduces the ability for a third party to cease all further data collection and output at any point by calling do_action( 'qm/cease' ), for example to prevent memory exhaustion during long-running operations
  • Reduces the width of the admin toolbar menu item by using lower decimal precision
  • Improves the Template panel information when a block theme is in use (for Full Site Editing)
  • Improves the performance and accuracy of stack traces and calling function information
  • Corrects some formatting of numbers and error messages in the REST API output
  • Adds more useful information when a persistent object cache or opcode cache isn’t in use
  • Improves clarity in the Scripts and Styles panels when any of the URLs include a port number
  • Introduces the qm/component_context/{$type} filter to complement qm/component_name/{$type} and qm/component_dirs
  • Improves internal code quality, internationalisation, and further reduces overall memory usage


  • Add a fallback for timing processing during Ajax requests that are dispatched before the shutdown hook.



  • Add WordPress memory usage statistic to Overview panel
  • Add block context information to the Blocks panel
  • Fix row highlighting of TH cells
  • Fix some panel resizing bugs


  • Implement a QM_DB_SYMLINK constant to prevent the db.php symlink being put into place.
  • Remove a dependency on SAVEQUERIES in the query collector.
  • Remove invalid scope attributes on table cells.


  • PHP 8 fix.
  • Improve the display for various empty values when logging.
  • Don’t display child menus until the parent menu is active. Makes the menu clearer.
  • Detect local host names in HTTP API requests and don’t mark them as ignoring certificate verification.
  • Prevent the text in toggle buttons from being selected when selecting data in tables.
  • Remove support for the Dark Mode plugin which isn’t Dark Mode any more.


  • Always show the Logs panel, with a link to help docs.
  • Whole bunch of improvements to QM’s “broken” state handling.
  • Remove usage of deprecated jQuery methods.
  • Add support for Altis dependencies as components.
  • Add innodb_buffer_pool_size variable to the mysql environment list.
  • Preformat the Logger output
  • Fix the PHP version check.


  • Correct an error introduced in 3.6.2 with the extra early error handling (ironic).


  • Correct the size of the close icon.


  • Capture and display the most recent PHP error that occurred before QM loaded.
  • Add support for the environment type added in WP 5.5.
  • Avoid a potentially blank translation for some plural forms.
  • Increase some contrast in dark mode.
  • Combine the response-related sections of the Request panel.
  • Add extra sanity checking when attempting to fetch the posix user information.


  • Adjust the bottom margin when the QM panel is open so QM doesn’t cover the bottom of the page. Works more often than not.
  • Prevent QM from triggering a fatal itself if a fatal occurs before the HTML dispatcher is loaded.
  • Add an informational message to the template output when template hooks are in use.
  • Fix errors caused by missing user or group IDs when collecting environment data.
  • Add TextMate to list of supported editors.
  • Demote some cache warnings to informational messages.
  • Support passing backtrace to QM_Backtrace.


  • Improvements to the UI when a fatal error occurs, including an admin toolbar warning.
  • Improvements to the UI when QM is running in “broken” mode due to missing jQuery or an unrecoverable JavaScript error.
  • Don’t display fatal errors if error display is off and the user cannot view QM.
  • Improvements to the visual appearance of the wp_die() output.
  • Simplify re-throwing a caught exception so QM doesn’t get the blame for fatal errors, eg. in the WordPress core fatal error handler.
  • Add support for logging a variable of any type in the logger, as a replacement for var dumping.
  • Don’t show a message for errors in Ajax calls that have already occurred on the main page load.
  • Don’t dispatch QM during an iframed request, eg the plugin info modal or an upgrader action.
  • Hide QM itself from various panels by default to remove noise. Can be controlled via the existing QM_HIDE_SELF configuration constant.
  • Support for the new is_favicon() conditional added in WP 5.4.
  • Fix the side panel resizing functionality.
  • Add a WP-CLI command for creating the symlink to the db file.
  • Add filters to QM_Util::get_file_dirs() and get_file_component() to allow support for non-standard plugin and theme locations.
  • Add an action that fires when QM enqueues its assets, so add-on plugins can enqueue theirs only when necessary.



  • Defer population of the found_formatted property because this can fire before WPML has initialised its locale proxy. Fixes #485.
  • Ensure all error types are accounted for when populating the panel menu error count. Fixes #486.


  • Add an editor selection UI on the Settings panel.
  • Improve the output of missing asset dependencies.
  • Improve the output of unsuccessful template parts.
  • Handle non-boolean constants such as WP_DEBUG_LOG, which now accepts a path too.
  • Add support for touch devices when resizing the panel. (Works alright-ish, probably needs some animation frame work.)
  • Apply the same styles to notices, deprecated, and strict errors.
  • Some more style resets for compatibility with popular themes.
  • Style changes to bring QM inline with WP 5.3’s improved button and focus styles.
  • More colour contrast and dark mode tweaks.
  • Add permalink-related filters to the concerned filters for the Request panel.
  • Fix and improve the admin toolbar menu hover colours.
  • Add the error count to the panel menu.
  • Remove unnecessary use of plural forms added in 3.4.0.
  • More CSS resets to avoid overly tall filters in Firefox.
  • Improved styling for warning rows.
  • Display the log count in the menu item.


  • Introduce an exception handler so a stack trace can be shown for fatal errors in PHP >= 7.
  • Add separate persistence of QM window for front-end and admin area.
  • Add the request and response HTTP headers to the Request panel.
  • Introduce Started and Stopped columns in the Timings panel.
  • By popular demand, revert back to closest first ordering of stack traces so they’re inline with most other dev tools out there.
  • Show the script handle in addition to the text domain in the Languages panel.
  • Improve the panel menu highlighting colours.
  • Better presentation of the default and current values for the settings constants.
  • Truncate long host names in the Scripts and Styles panels.
  • Add some more of the admin screen globals to the admin collector.
  • Switch back to using a monospace font in numeric data cells.
  • Allow dark mode to be enabled with QM_DARK_MODE.
  • Display the total query count even when SAVEQUERIES is defined as false.
  • Allow proper plural forms to be used wherever a phrase includes a numeric value.
  • More style resetting for compatibility with Twenty Twenty.
  • Avoid a division by zero when cache hits is 0.
  • Switch to (mostly) CSS for the child menu item marker.


  • Expose instances where a requested template part was not loaded.
  • Update the docs for multiple wpdb instances.
  • Various accessibility improvements.
  • Remove the RDBMS info as it’s not at all reliable.


  • Fix a compatibility issue where QM and the fatal error protection in WordPress 5.2+ were handling syntax errors differently.
  • Fix some bugs with the icons for the panel controls.