Jesper van Engelen

The Sidebars & Widgets extension for the Debug Bar shows you all you need to know about the sidebars and widgets on the current page. It shows the sidebars displayed and the widgets displayed in them, and tells you whether all widgets in the sidebar were actually displayed.
This plugin allows you to analyze the behaviour of your WordPress sidebars and wigets, and is aimed at WordPress developers.
<blockquote>
This plugin is an extension to the <a href="https://wordpress.org/plugins/debug-bar/" rel="ugc">Debug Bar plugin</a>, which is required for this plugin to work.
</blockquote>
This plugin integrates nicely with <a href="https://wordpress.org/plugins/content-aware-sidebars/" rel="ugc">Content Aware Sidebars</a>, telling you what sidebars were replaced and merged. It is an essential plugin if you use Content Aware Sidebars with a big number of sidebars.

Debug Bar – Sidebars & Widgets

Debug Bar extension that adds information about the sidebars and widgets on the current page. Integrates with Content Aware Sidebars 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 – Sidebars & Widgets vs BlackBox Debug Bar