The WordPress debug log: how to turn it on, find it and read it

Turn it on without showing errors to visitors

WordPress’s documentation gives these lines for wp-config.php, the configuration file in your site’s main folder:

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

// 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 );

The documentation says what they do: they “log all errors, notices, and warnings to a file called debug.log in the wp-content directory. It will also hide the errors, so they do not interrupt page generation.” And where they go: “You must insert this BEFORE /* That’s all, stop editing! Happy blogging. */ in the wp-config.php file.” (developer.wordpress.org) The comment has changed over the years: in WordPress 7.1.2’s sample file it reads “That’s all, stop editing! Happy publishing.”, and the line above it says: “Add any custom values between this line and the “stop editing” line.” (WordPress 7.1.2 source)

Where the log file is

“When set to true, the log is saved to debug.log in the content directory (usually wp-content/debug.log) within your site’s file system. Alternatively, you can set it to a valid file path to have the file saved elsewhere.” (developer.wordpress.org)

A file in wp-content sits in the public part of your site, and on many servers anyone who knows its address can open it. A path outside the web folder avoids that. Your host can tell you which folder is safe:

define( 'WP_DEBUG_LOG', '/tmp/wp-errors.log' );

Open the file with your hosting panel’s File Manager or by FTP, and read it from the bottom: the newest entries are last.

debug.log not created? The usual causes

The first cause is easy to miss, because PHP only warns and keeps the first value:

<?php
define( 'WP_DEBUG', false ); // already further up in wp-config.php

// ... added later, lower down:
define( 'WP_DEBUG', true );

echo 'WP_DEBUG is ', var_export( WP_DEBUG, true ), "\n";

Warning: Constant WP_DEBUG already defined, this will be an error in PHP 9 in /var/www/html/wp-config.php on line 5
WP_DEBUG is false

How to read an entry

Each entry is one message from PHP: what went wrong, then the file and line. This is a real fatal error, from a plugin that still uses a function PHP 8.0 removed:

Fatal error: Uncaught Error: 1Call to undefined function create_function() in /var/www/html/2wp-content/plugins/old-slider/includes/slider.php:3
Stack trace:
#0 {main}
  thrown in /var/www/html/wp-content/plugins/old-slider/includes/3slider.php on line 3

In the log file, each entry also starts with the date and time, and the kind of message with “PHP” in front, for example [01-Oct-2026 17:53:48 UTC] PHP Warning: (from our test site, WordPress 7.1.2). Three kinds of message matter most:

• Fatal error: the page stopped. Fix these first; the critical error guide shows how.
• Warning: something went wrong, but the page carried on.
• Deprecated: works today, but a future PHP version will change it. Not urgent; the plugin’s next update usually fixes it. What each level means is in deprecation notice vs fatal error.

Search the log for the plugin’s folder name to see everything one plugin caused. Some messages only appear on certain pages or with certain data, such as “count(): Argument #1 ($value) must be of type Countable|array”: keeping the log on for a few days after a PHP update catches them.

When you’re done

The documentation is clear: “It is not recommended to use WP_DEBUG or the other debug tools on live sites; they are meant for local testing and staging installs.” (developer.wordpress.org) Once you’ve found the problem, set WP_DEBUG back to false and delete the log file.