How to Debug WordPress Issues: A Developer’s Troubleshooting Guide

WordPress sites break. Plugins conflict, updates go wrong, server configurations change, and code that worked yesterday stops working today. The difference between a frustrating day and a quick fix is having a systematic approach to finding the problem.

This guide covers the debugging tools and techniques every WordPress developer should know, organized by the type of problem you are likely to encounter.

Enable WordPress Debugging

WordPress has a built-in debugging system controlled by constants in your wp-config.php file. These are the essential ones to know.

Setting WP_DEBUG to true tells WordPress to display PHP errors, warnings, and notices that are normally hidden. This is the first thing to enable when troubleshooting any issue. The WP_DEBUG_LOG constant, when set to true, writes all debug messages to a file at wp-content/debug.log instead of displaying them on screen — essential for debugging on a live site where you do not want visitors seeing error messages. WP_DEBUG_DISPLAY should be set to false on production sites to prevent errors from being shown to visitors, even when logging is enabled.

Additionally, setting SCRIPT_DEBUG to true forces WordPress to use the unminified versions of its CSS and JavaScript files, which is useful when debugging frontend issues in core or plugin assets.

After making changes, always check the debug.log file. It often contains the exact error message and file location that points you directly to the problem.

The White Screen of Death

The white screen — a completely blank page with no error message — is usually caused by a PHP fatal error that occurs before WordPress can render any output. When the screen is white and debug logging is not yet enabled, you need to access your server through SFTP or your hosting file manager to edit wp-config.php.

Enable WP_DEBUG and WP_DEBUG_LOG, then reload the page. If the screen is still white, check wp-content/debug.log for the fatal error. Common causes include a plugin calling a function that does not exist (often after an incomplete update), a theme file with a syntax error, or running out of PHP memory.

If you cannot access the admin at all, rename the active theme’s folder via SFTP to force WordPress to fall back to a default theme. If that fixes it, the problem is in your theme. If not, rename the plugins folder to plugins-disabled to deactivate all plugins. If the site loads, rename the folder back and reactivate plugins one at a time to identify the culprit.

Plugin Conflicts

Plugin conflicts are the most common source of WordPress problems. Two plugins hooking into the same function, loading incompatible JavaScript libraries, or modifying the same data can produce anything from subtle visual glitches to complete site crashes.

The systematic approach is straightforward. Deactivate all plugins. If the problem disappears, reactivate plugins one at a time, testing after each activation. When the problem returns, you have found the conflicting plugin. Often the conflict is between two specific plugins rather than a single faulty one — in that case, you will need to narrow down which combination causes the issue.

Check the error log during this process. Conflict errors often include both plugin names in the stack trace, which saves you from testing every combination manually.

Database Issues

Database problems manifest as missing content, broken settings, corrupted tables, or slow queries. WordPress provides a built-in database repair tool that you can enable by adding WP_ALLOW_REPAIR set to true in wp-config.php, then visiting yoursite.com/wp-admin/maint/repair.php. This tool can repair and optimize corrupted tables.

For deeper database issues, use phpMyAdmin or the command line to inspect tables directly. Check the wp_options table for corrupted autoloaded options, which are a common cause of slow page loads. The wp_options table should not have more than a few megabytes of autoloaded data — if it does, some plugin is storing excessive data there, and you need to identify and clean it up.

Always back up your database before making any direct changes. A single wrong query can destroy data that is difficult or impossible to recover.

Permalink and Rewrite Issues

If your pages return 404 errors even though the content exists, the likely cause is corrupted rewrite rules. Go to Settings > Permalinks in the WordPress admin and click “Save Changes” without changing anything. This regenerates the rewrite rules and fixes most permalink issues.

If that does not work, check your .htaccess file (on Apache servers) or Nginx configuration. WordPress needs specific rewrite rules in these files to handle pretty permalinks. If the file is missing, empty, or has been modified by another application, permalinks will break.

Memory Exhaustion Errors

The error “Allowed memory size of X bytes exhausted” means a PHP script tried to use more memory than the server allows. This can be caused by a plugin processing large datasets, an image manipulation operation on a very large file, or a code loop that does not terminate properly.

Increasing the memory limit is a temporary fix. Add WP_MEMORY_LIMIT to wp-config.php set to a value like 256M or 512M. However, if a plugin or theme consistently needs hundreds of megabytes of memory, that is a code quality issue that should be addressed rather than accommodated.

Performance Debugging

When your site is slow, you need to identify where the time is being spent. The Query Monitor plugin is the most valuable tool for this. It displays all database queries on each page load, including which plugin or theme triggered each query, how long it took, and whether it is a duplicate or slow query.

Query Monitor also shows HTTP API requests (calls to external services that can block page rendering), hooks and their execution order, PHP errors, and enqueued scripts and styles. Install it on staging or development environments to diagnose performance issues without affecting your live site.

For server-level performance, your hosting provider’s access logs and error logs provide request timing data. A slow time-to-first-byte (TTFB) indicates server-side processing problems, while a fast TTFB with slow page completion suggests frontend issues like large images or render-blocking scripts.

Email Delivery Problems

WordPress uses PHP’s mail() function by default, which is unreliable on many hosting environments. If contact forms or notification emails are not arriving, install an SMTP plugin like WP Mail SMTP and configure it to send through a proper email service (Gmail SMTP, SendGrid, Mailgun, or your hosting provider’s SMTP server).

Enable the plugin’s email logging feature to verify whether emails are actually being sent or failing silently. Common causes of email failures include the hosting server’s IP being blocklisted, missing SPF and DKIM DNS records for your domain, and the FROM address not matching a domain you control.

Version Control and Staging

The best debugging strategy is prevention. Use a staging environment that mirrors your production site to test updates, new plugins, and code changes before they go live. Many managed hosts provide one-click staging. If yours does not, a local development environment using tools like LocalWP or DevKinsta lets you test safely on your own machine.

Keep your custom code in version control using Git. When something breaks, you can compare the current code to the last working version and identify exactly what changed. Without version control, debugging code changes means relying on memory, which is unreliable at best.

Debugging is not a talent — it is a process. Enable logging, isolate variables, test systematically, and let the error messages guide you. Every WordPress problem has a cause, and with the right tools and approach, you can find it.