WordPress Debuging: A Complete Guide

In this post, we’ll dig into the built-in WordPress debug mode and show you how to enable it. Then, we’ll also share some of the other ways in which you can debug your WordPress site.

Here’s what we’ll cover:

• An introduction to WordPress debug mode and the debug log
• How to enable WordPress debug mode (three methods)
• Some other ways to debug WordPress

 

What Does WP Debug Do?

The core WordPress software is written in PHP, as are plugins and themes. If you’re having issues with your site, WordPress debug mode can help you find out what’s going wrong by displaying all PHP errors, notices, and warnings.

Once you enable debug mode, you’ll see messages like this whenever there’s an issue (even if it’s not causing immediate problems)

You can then fix the problem or report it to your developer or the theme/plugin’s developer.

 

Further reading:

How Not to Hurt Your Visitors When Using the WordPress Maintenance Mode

How to Get Best Speed Performance with WordPress

How to Maintain a Healthy WordPress Website

How to Reduce Security Risks From WordPress Plugins

How to Test a WordPress Backup Before Restoring

Recommended Caching Plugins for Your WordPress Website

WordPress Maintenance Tasks You Need to Perform Regularly

WordPress Performance: How to Find a Slow Plugin

WordPress Security Plugins Compared to Find Which Works Best

WordPress Security: The Complete Guide

WordPress Security: The SQL Injection

 

What Is the WordPress Debug Log?

When you enable WordPress debug mode by itself, you’ll see messages on your site at the moment – but those messages won’t be saved anywhere.

If you want to save them, you can also enable the WordPress debug log to save all of those messages and errors to a file on your server.

When enabled by setting the WP_DEBUG_LOG constant to true, WordPress will write all issues to the following file:

wp-content/debug.log

However, you can also specify a custom file path to write the log to a different location on your server.

If you want to save problems to the log but not publicly display them within the HTML of your pages, you can also use the WP_DEBUG_DISPLAY constant to keep debug mode enabled but not display messages on your site.

Typically, you’ll want to combine WP_DEBUG_DISPLAY with WP_DEBUG_LOG.

How to Enable WordPress Debug Mode

To enable WordPress debug mode, you have several options. We’ll cover two methods to enable it:

 

How to Use a WordPress Debug Plugin

You can also find free WordPress debug plugins that make it easy to enable debug mode. There are several options at WordPress.org, but we recommend the free WP Debugging plugin from Andy Fragen.

Once you install and activate the plugin, it starts working right away. By default, it sets the following constants to true (that is, it enables the following features):

• WP_DEBUG – enables debug mode.
• WP_DEBUG_LOG – saves messages to a log file.
• SCRIPT_DEBUG
• SAVEQUERIES

We’ll cover what the last two constants do a little later on in this post.

To configure a few options, you can go to Tools → WP Debugging:

Once you’re finished, make sure to disable the plugin to disable debug mode.

 

How to Manually Enable WordPress Debug Mode

You can also enable WordPress debug mode by manually adding the constants to your wp-config.php file.

To get started, connect to your server via FTP and edit the wp-config.php file. By default, this file is in the root folder of your site (unless you moved it for security reasons).

To enable just the basic WordPress debug mode, add the following code snippet above the line that says /* That’s all, stop editing! Happy blogging. */:

// Enable WP_DEBUG mode
define( 'WP_DEBUG', true );

You can also use some of the following constants according to your preferences:

// Enable Debug logging to the /wp-content/debug.log file
define( 'WP_DEBUG_LOG', true );
// Disable display of errors and warnings
define( 'WP_DEBUG_DISPLAY', false );
@ini_set( 'display_errors', 0 );

Once you’re finished, you can either set the constants to false or just remove the snippet to disable debug mode.

 

Further reading:

How Not to Hurt Your Visitors When Using the WordPress Maintenance Mode

How to Get Best Speed Performance with WordPress

How to Maintain a Healthy WordPress Website

How to Reduce Security Risks From WordPress Plugins

How to Test a WordPress Backup Before Restoring

Recommended Caching Plugins for Your WordPress Website

WordPress Maintenance Tasks You Need to Perform Regularly

WordPress Performance: How to Find a Slow Plugin

WordPress Security Plugins Compared to Find Which Works Best

WordPress Security: The Complete Guide

WordPress Security: The SQL Injection

 

Make Sure to Disable Debug Mode in WordPress When You’re Finished

The debug mode is useful when you’re trying to troubleshoot problems with WordPress, but you shouldn’t leave it enabled 24/7 because it can reveal text from your PHP code to website visitors.

We mentioned this above – but this is just a reminder to always disable debug mode when you’re finished troubleshooting.

 

Other Ways to Debug WordPress

Beyond the built-in debug tool that we featured above, there are several other built-in and third-party tools to help you debug your WordPress site.

 

Script Debug

SCRIPT_DEBUG is another built-in constant that forces WordPress to use the dev versions of core CSS and JavaScript files instead of the minified versions that it usually loads.

This can be helpful if you’re testing changes to the built-in .js or .css files.

To enable SCRIPT_DEBUG, you can either:

• Use the free WP Debugging plugin from above, which enables it by default.
• Add the following constant to your wp-config.php file – define( 'SCRIPT_DEBUG', true );

 

Database Query Debugging

If you’re having issues with your site’s database, you can enable database query logging using the SAVEQUERIES constant to track:

• Each database query.
• The function that called the database query.
• How long the query took.

To enable query logging, you can either:

• Use the free WP Debugging plugin from above, which enables it by default.
• Add the following constant to your wp-config.php file – define( 'SAVEQUERIES', true );

Note: this will impact your site’s performance so try to use it on a staging site whenever possible and disable it as soon as you’re finished.

 

Query Monitor Plugin

The Query Monitor plugin is a free plugin that’s helpful for debugging a number of different areas in WordPress including:

• Database queries.
• PHP errors.
• Hooks and actions.
• Block editor blocks.
• Enqueued scripts and stylesheets.
• HTTP API calls.
• User capabilities.

Overall, it’s one of the best WordPress debug tools that you’ll find, which is why it has almost a perfect 5-star rating on over 320 reviews.

Once you install and activate the plugin, you’ll get some new options on the WordPress toolbar that display debug information. When clicked, those options will open a new Query Monitor box that gives you more information:

 

 

 

New Relic

New Relic is a premium tool for analyzing and debugging your site’s performance. It can help you discover bottlenecks and issues that are affecting your site’s performance.

 

Server Logs

Finally, your server logs can also be a useful tool in debugging WordPress.

You’ll need to consult your host’s documentation to learn where you can access your server logs.

 

Summary

If you need to debug WordPress, the built-in WordPress debug mode provides a useful way to view PHP errors and notices.

You can enable it with plugins or by adding code snippets to your site’s wp-config.php file.

For more help, you can also use other built-in tools or third-party tools like New Relic and the free Query Monitor plugin.

Do you have any other questions about how to debug WordPress? Leave a comment and let us know!