Query Monitor is the developer tools panel for WordPress. It enables you to debug database queries, PHP errors, hooks and actions, block editor blocks, enqueued scripts and stylesheets, rewrite rules, HTTP API calls, and much more.
It focuses on presenting information in a useful manner, for example by showing aggregate database queries grouped by the plugins, themes, or functions that are responsible for them, allowing you to quickly determine poorly performing plugins, themes, and functions.
Query Monitor is free and open source software, just like WordPress.
For more information: