horike

Displays Super Global valiables for the current request.Like $_POST, $_GET, and $_COOKIE. Requires the debug bar plugin.

Debug Bar Super Globals

Hasn't received any updates in 8 years and it STILL WORKS!

Still Works (as of WordPress 5.5)

Displays Super Global valiables for the current request.Like $_POST, $_GET, and $_COOKIE. Requires the debug bar plugin.

Greg Winiarski

BlackBox is symfony like unobstrusive debug bar attached to the top of the browser window.
How can it help you with development: 
1. instantly inspect global variables (GET, POST, COOKIE, SERVER) 
2. debug both frontend and admin area 
3. executed MySQL queries and time it took to execute each query (useful for finding slow queries) 
4. profiler for measuring performance of your plugins and themes 
5. errors occurred when loading WordPress page

BlackBox Debug Bar

Immediate feedback on a great majority of errors. Added a conditional red background to the Errors, and with this modification I have never miss even a notice anymore.

Thank you very much!

Essential plugin in my developer toolset

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

Debug Bar Super Globals vs BlackBox Debug Bar