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Query Monitor – The developer tools panel for WordPress

By John Blackbourn

Developer Tools & Customization / Debugging & Development Tools

Query Monitor – The developer tools panel for WordPress Review - In-Depth Analysis

Query Monitor is the developer tools panel for WordPress and WooCommerce. It enables debugging of database queries, PHP errors, and more.

Performance Overview

WPS Score

7.01/10

User Rating

4.9/5 (based on 467+ reviews)

Active Installations

200,000+

Update Frequency

Outstanding It is calculated using the weighted average of same category plugins.

Security Score

7.1 / 10 (High Risk) It is calculated using the weighted average of all versions.

What It Does

Query Monitor is the developer tools panel for WordPress and WooCommerce. 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.

Query Monitor supports versions of WordPress up to three years old, and PHP version 7.4 or higher.

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.
Usage of 'Doing it Wrong' or 'Deprecated' functionality in the code on your site.
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.
Usage of switch_to_blog() and restore_current_blog() on Multisite installations.

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 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.

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.

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 aims to be fully accessible to all of its users.

Comparing to Alternatives

Query Monitor stands out among WordPress developer tools by offering comprehensive debugging features integrated directly into the admin bar. Compared to alternatives like Debug Bar, it provides more detailed insights and a richer interface.

Top alternatives

Debug Bar ( WPS: 7.12)

Strengths

Extensive debugging information including database queries, hooks, and HTTP requests.
Lightweight enough to run on production sites without significant overhead.
User-friendly interface integrated into the admin bar for quick access.
Detailed error and performance tracking aiding in rapid issue resolution.

Weaknesses

Requires adding /wp-content/db.php to .gitignore to avoid version control conflicts.
May have compatibility issues with plugins that use custom database handlers like WP Studio.
No official pro version with extended features.
Some users report challenges when integrating with certain hosting environments.

User Sentiment Analysis

Users consistently praise Query Monitor for its indispensable role in debugging and performance monitoring, highlighting its ease of use and depth of information.

Positive highlights

"I can't imagine debugging WordPress sites without it anymore." - Mehraz Morshed
"An indispensable tool for developers." - dochara
"A fantastic tool for troubleshooting database issues!" - casualadam
"Provides insight into what is happening, shows errors, and gives stats and timings." - dmccan
"Probably the best tool for theme and plugins developers." - Attila Bogozi

Common complaints

Needs manual exclusion of db.php in version control systems.
Incompatibility with some plugins using custom database solutions.
Limited official support or updates for edge cases.
No premium version to unlock additional features.

Weaknesses

Lack of pro version limits advanced feature availability.
Some users experience integration issues with specific development environments.

Who Should Use This?

Best for

Developers and site administrators who need a powerful, detailed debugging and performance monitoring tool integrated into WordPress.

Not ideal for

Users looking for a simple, non-technical plugin or those requiring official premium support and extended features.

Pricing & Value

Free version includes

The free version offers comprehensive developer tools including query analysis, error logging, hooks and actions tracking, and HTTP request monitoring, all accessible via the admin bar.

Final Verdict

Query Monitor is an exceptional free tool that provides deep insights into WordPress site performance and debugging, making it invaluable for developers.

While it lacks a pro version, its extensive features and lightweight design make it a top choice for anyone needing detailed diagnostic information without additional cost.