Debugging WordPress

Debug WordPress with wp-env, Xdebug and PhpStorm @wordpress/env (wp-env) starts a complete WordPress development environment in Docker with one command, with the current plugin or theme mounted inside. It also has Xdebug built in: one flag enables it, and PhpStorm (or VS Code) can then stop at breakpoints in your plugin, step through the code…

A WordPress debugging setup per environment Debug settings are toggled in wp-config.php by hand, forgotten on, and then a production site shows notices to visitors or fills a public debug.log. A small setup decides everything from the environment type: on local and staging, full logging into a private file and visible errors where useful; on…

Query Monitor: find what makes a WordPress page slow A slow page has a cause somewhere between the database, PHP code, hooks and external HTTP requests. Query Monitor is a free debugging plugin that shows all of this for the current request in a panel under the admin bar: every database query with its time…

Add static analysis with PHPStan to WordPress plugin development PHPStan reads PHP code and finds bugs without running it: calling a method on something that can be null or a WP_Error, passing the wrong type to a function, using an undefined variable, a missing array key. It infers types from native declarations, docblocks and function…

Catch synchronous and async JavaScript errors with try/catch, window.onerror and unhandledrejection to prevent silent failures in WordPress themes.

Learn how to read MySQL EXPLAIN output to identify missing indexes and eliminate full-table scans.

Add your own checks to the Site Health screen Tools → Site Health, added in WordPress 5.2, checks the PHP version, HTTPS, scheduled events, the REST API and more, and shows the results as good, recommended or critical. Plugins can add their own tests with the site_status_tests filter. That is the right place to tell…

WP_Error: return errors the WordPress way A function that returns false on failure tells the caller that something went wrong, but not what. WordPress has its own error object for this, WP_Error: it carries an error code, a message and optional data, and it can hold several errors at once. Core functions such as wp_insert_post(),…

AJAX and JSON: json_decode() returns null in WordPress You pass an array from PHP with json_encode() through AJAX, and on the other side json_decode() returns null, or the data has the wrong types. In my case the cause was in the data itself: numbers that were strings instead of integers. Below is that case, and…