DevTools Classes & Attributes Panel is a free Chrome add-on developed by Gustavo Sillero. It is designed to enhance the functionality of the Elements panel in Chrome's DevTools. With this add-on, users can easily toggle and edit classes, attributes, and states such as checked and selected.

The add-on provides an extra sidebar on the Elements panel, allowing users to quickly access and modify classes and attributes. This can be particularly useful for web developers and designers who frequently work with HTML and CSS. By providing a convenient way to toggle and edit classes and attributes, DevTools Classes & Attributes Panel streamlines the debugging and editing process, saving users time and effort.

Overall, DevTools Classes & Attributes Panel is a valuable tool for Chrome users who frequently work with web development. Its ability to quickly toggle and edit classes, attributes, and states makes it a useful addition to the DevTools arsenal.