/handbook/developing-for-block-editor-and-site-editor/debugging-configurations/
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Resources Developing for Block Editor and Site Editor Improving developer experience Debugging configurations
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On this page
Query Monitor (QM) Plugin, WP_DEBUG Constants, and Xdebug
a. Query Monitor Plugin
b. WP_DEBUG Constants
c. Enabling Xdebug
Redux DevTools for Gutenberg Block Development
a. State Monitoring
b. Time-Travel Debugging
c. Action Comparison
Getting Started with Redux DevTools
Last updated on Mar 31, 2026
Debugging Configurations
Debugging is a crucial part of the development process, and WordPress offers several built-in tools and external utilities to streamline debugging. Two primary areas of focus in WordPress debugging are using the Query Monitor (QM) plugin and WP_DEBUG constants, alongside advanced tools like Xdebug for deeper debugging. For JavaScript-heavy parts of the Gutenberg editor, tools like Redux DevTools can be invaluable for debugging the state and actions of blocks.
Query Monitor (QM) Plugin, WP_DEBUG Constants, and Xdebug
When it comes to debugging in WordPress development, using tools like Query Monitor, WP_DEBUG constants, and Xdebug is essential for diagnosing issues efficiently. The Query Monitor plugin provides detailed insights into database queries, PHP errors, and hooks. WP_DEBUG constants offer customizable error logging, enabling better control over the debugging process. For deeper debugging, Xdebug integrates with your IDE, allowing breakpoints, step-through execution, and performance profiling. Combined, these tools form a robust debugging environment for any WordPress project.
a. Query Monitor Plugin
The Query Monitor (QM) plugin is an essential tool for WordPress developers, offering insights into various parts of a WordPress application. It provides information on database queries, PHP errors, hooks, scripts, styles, and more. Here’s how it helps with debugging:
- Database Queries: QM lists all queries run on a page, including the time taken for each query, the specific query string, and the file that triggered it. This helps identify slow queries or redundant database calls.
- PHP Errors and Warnings: It captures and displays any PHP notices, warnings, or fatal errors occurring on the page. Unlike PHP logs, it shows these errors directly in the WordPress admin or front end for easy access.
- Hooks and Actions: QM provides a detailed view of all hooks and actions that fire during a page load, helping you trace how and where certain functionality is triggered.
- Enqueued Scripts and Styles: You can easily debug which scripts and styles are loaded on a page, along with their dependencies. This is particularly helpful for debugging block editor-related issues with asset management.
- HTTP API Calls: QM tracks outgoing HTTP requests made via the WordPress HTTP API, showing the request URL, method, and response status.
b. WP_DEBUG Constants
WordPress provides several constants to enable debugging at different levels. These constants are set in the wp-config.php file:
WP_DEBUG: The core constant for debugging. When set totrue, WordPress displays all PHP errors, notices, and warnings on the screen. Example usage:
define( 'WP_DEBUG', true );
WP_DEBUG_LOG: When enabled, it writes all debug messages to adebug.logfile in the/wp-content/directory, without displaying them on the screen. This is useful for production environments where you don’t want to expose error details to users.
define( 'WP_DEBUG_LOG', true );
WP_DEBUG_DISPLAY: Controls whether debug messages are displayed in the HTML of pages. This can be disabled when usingWP_DEBUG_LOGto ensure errors are only logged.
define( 'WP_DEBUG_DISPLAY', false );
SCRIPT_DEBUG: Forces WordPress to use non-minified versions of core CSS and JavaScript files. This is crucial for debugging issues with the WordPress block editor or any JS-related functionality.
define( 'SCRIPT_DEBUG', true );
JETPACK_DEV_DEBUG: By disabling Jetpack dev debug mode on a local environment, you can access Jetpack-related articles for development/debugging.
define( 'JETPACK_DEV_DEBUG', false );
For more reference, please visit Debugging in WordPress.
c. Enabling Xdebug
Xdebug is a PHP extension that offers powerful debugging capabilities, such as breakpoints, stack traces, and performance profiling. It integrates with most modern IDEs like PhpStorm and Visual Studio Code.
Here’s a quick overview of Xdebug’s benefits for WordPress:
- Breakpoints: Set breakpoints in your PHP code, which pause execution at a specific line, allowing you to inspect variables, the call stack, and objects.
- Step Debugging: Step through your code line by line, helping you understand how it’s executing and where things may be going wrong.
- Profiling: Xdebug provides performance profiling, which outputs data that can be visualized using tools like Webgrind. This helps in identifying bottlenecks in your code, such as slow database queries or memory-heavy operations.
To enable Xdebug in a development environment:
- Install Xdebug (via
pecl install xdebugor through your package manager). - Configure your
php.ini:
zend_extension=xdebug
xdebug.mode=debug
xdebug.start_with_request=yes
xdebug.client_port=9003
- Configure your IDE to listen on the specified port and start debugging your WordPress application.
Redux DevTools for Gutenberg Block Development
Gutenberg uses the Redux state management library under the hood to handle the editor’s state. For developers working on custom blocks, understanding how state changes occur is critical. Redux DevTools is a browser extension that allows you to inspect, monitor, and time-travel through state changes in your Gutenberg blocks.
Here’s how Redux DevTools aids in Gutenberg block development:
a. State Monitoring
When building custom blocks, you may use the wp.data API to manage state, such as updating block attributes, handling block selection, or syncing data between blocks. Redux DevTools helps you see how this state changes in real time:
- State Tree: View the entire state of the editor at any point. This is particularly useful for debugging how your block’s attributes or inner states are managed.
- Action History: Redux DevTools tracks all dispatched actions, showing what actions have occurred, such as
UPDATE_BLOCK_ATTRIBUTESorSELECT_BLOCK. You can examine which actions were triggered when a user interacts with the editor, which can help in diagnosing issues related to user input or changes in block settings.
b. Time-Travel Debugging
One of the unique features of Redux DevTools is time-travel debugging. You can “rewind” the editor to a previous state and see how it looked at any given point in time. This is especially useful for:
- Testing State Changes: You can try different interactions, inspect how the state changes, then rewind and try again. This helps in ensuring that your block behaves as expected under different scenarios.
- Undo/Redo Analysis: Gutenberg’s editor supports undo/redo functionality. Redux DevTools can show you how state reverts or advances when these actions are triggered, allowing you to debug any issues related to the undo/redo process.
c. Action Comparison
Redux DevTools also allows you to compare different states before and after an action is dispatched. This is particularly helpful when debugging complex interactions in custom blocks that depend on multiple attributes or store interactions.
For example, when a user changes the alignment of a block, you can inspect the exact changes that were made to the state and compare the pre-action and post-action state trees.
Getting Started with Redux DevTools
- Install the Redux DevTools browser extension (available for Chrome, Firefox, etc.).
- Ensure that your environment supports Redux debugging by enabling
wp.datalogging:
wp.data.use( wp.data.plugins.logger );
- Open the DevTools, go to the “Redux” tab, and inspect the state, actions, and time-travel features.
Version control and compatibility
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