Black Bar

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.

Log/Debug the PHP code in your Theme/Plugin with your Browser Console (no extension needed)

BlackBox is a plugin for plugin and theme developers. It collects and displays useful debug information (errors, executed queries, globals, profiler).

Query Monitor is the developer tools panel for WordPress and WooCommerce.

Debug Bar Post Types adds a new panel to the Debug Bar with detailed information about registered post types. Requires "Debug Bar" plugin.