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

Debug Bar Constants adds three new panels to the Debug Bar that display the defined constants available to you as a developer for the current request:
<ul>
<li>WP Constants</li>
<li>WP Class Constants</li>
<li>PHP Constants</li>
</ul>
<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-constants" 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-constants" rel="ugc">Support Forum</a> or in the <a href="https://github.com/jrfnl/Debug-Bar-Constants/issues" rel="nofollow ugc">GitHub repository</a>.

Debug Bar Constants

Debug Bar Constants adds three new panels to the Debug Bar that display the defined WP and PHP constants for the current request.

BlackBox Debug Bar vs Debug Bar Constants