Query Monitor is the developer tools panel for WordPress. It includes some advanced features such as Ajax and REST API debugging, and the ability to narrow down its output by plugin or theme.
Query Monitor focuses heavily on presenting its information in a useful manner. For example, aggregate database query information is made available, allowing you to quickly determine poorly performing plugins, themes, or functions. It adds an admin toolbar menu showing an overview of the current page, with complete data shown in a panel once you select a menu item.
Query Monitor is free and open source software, just like WordPress.
For more information, please see: