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).

Juliette Reinders Folmer

Subharanjan

This plugin adds two more tabs in the Debug Bar to display hooks(Actions and Filters) attached to the current request. Actions tab displays the actions hooked to current request. Filters tab displays the filter tags along with the functions attached to it with respective priority.
<h4>Important</h4>
This plugin requires the <a href="https://wordpress.org/plugins/debug-bar/" rel="ugc">Debug Bar</a> plugin to be installed and activated.
Also note that this plugin should be used solely for debugging and/or in a development environment and is not intended for use on a production site.
If you like this plugin, please <a href="https://wordpress.org/support/view/plugin-reviews/debug-bar-actions-and-filters-addon" rel="ugc">rate and/or review</a> it. If you have ideas on how to make the plugin even better or if you have found any bugs, please report these in the <a href="https://wordpress.org/support/plugin/debug-bar-actions-and-filters-addon" rel="ugc">Support Forum</a> or in the <a href="https://github.com/subharanjanm/debug-bar-actions-and-filters-addon/issues" rel="nofollow ugc">GitHub repository</a>.

Debug Bar Actions and Filters Addon

Awesome

Displays all the hooks( Actions and Filters ) for the current request in Debug Bar panel.

BlackBox Debug Bar vs Debug Bar Actions and Filters Addon