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).

Chris Hardie

Debug Bar Widgets adds a new panel to the <a href="https://wordpress.org/extend/plugins/debug-bar/" rel="ugc">Debug Bar</a> that displays all registered widgets.
It could be helpful to developers who want to check whether custom widgets are registering properly.
This plugin requires that the Debug Bar plugin be installed and activated.
Want to help make this plugin better? <a href="https://github.com/ChrisHardie/debug-bar-widgets" rel="nofollow ugc">Pull requests are welcome</a>.

Debug Bar Widgets

Debug Bar Widgets adds a new panel to the Debug Bar that displays all registered widgets.

BlackBox Debug Bar vs Debug Bar Widgets