WebDiff is a free Chrome add-on developed by popov654. It falls under the category of Browsers and specifically the subcategory of Add-ons & Tools. This simple tool is designed to compare HTML output before and after making changes in the backend, such as refactoring.

With WebDiff, users can easily identify any differences in the HTML output by comparing the pre and post-change versions. This can be particularly useful for developers who want to ensure that their changes have not introduced any unexpected issues or inconsistencies in the HTML code.

Currently, WebDiff allows users to compare the post-processed HTML, which includes the output after all JavaScript code has been executed. However, the developer has plans to include the ability to compare the page's visual representation in future releases.

Overall, WebDiff provides a straightforward and efficient way to compare HTML output and ensure the integrity of the code after making backend changes.