Query Monitor is the developer tools panel for WordPress.
Black Bar is an unobtrusive Debug Bar for WordPress developers that attaches itself to the bottom of the browser window.
Debug Bar Rewrite Rules adds a new panel to Debug Bar that displays information about WordPress Rewrites Rules (if used).
Extends the Query Monitor and Debug Bar plugins for ElasticPress queries.
Extends the debug-bar plugin with additional tabs to measure runtimes between checkpoints and lookup variable content.
Debug Bar Cron adds a new panel to Debug Bar that displays information about WP scheduled events.
Displays all the hooks( Actions and Filters ) for the current request in Debug Bar panel.
Log/Debug the PHP code in your Theme/Plugin with your Browser Console (no extension needed)
Debug Bar List Script & Style Dependencies is an add-on to WordPress Debug Bar
Debug Bar Post Types adds a new panel to the Debug Bar with detailed information about registered post types. Requires "Debug Bar" plugin.
BlackBox is a plugin for plugin and theme developers. It collects and displays useful debug information (errors, executed queries, globals, profiler).
Debug Bar Transients adds a new panel to Debug Bar that displays information about WordPress transients.
Debug Bar Shortcodes adds a new panel to the Debug Bar that displays the registered shortcodes for the current request.
Debug Bar Constants adds three new panels to the Debug Bar that display the defined WP and PHP constants for the current request.
Displays the current rewrite rules for the site. Requires the debug bar plugin.