Html Validator is a Firefox browser extension designed to enhance web development by providing HTML validation directly in the browser. This tool integrates seamlessly with Firefox, allowing users to view the number of HTML errors on a webpage through an icon in the status bar, while detailed error descriptions can be accessed by inspecting the HTML source. Built on the robust Tidy and OpenSP algorithms, Html Validator ensures that validation is performed locally, safeguarding user privacy by avoiding third-party server interactions.

The extension categorizes HTML issues into three distinct groups: errors that cannot be fixed, warnings that can be automatically corrected, and optional accessibility warnings based on W3C guidelines. This structured approach helps developers identify and rectify issues effectively, ensuring adherence to web standards and enhancing overall page quality. Html Validator is a valuable tool for developers seeking to improve their web pages' compliance and accessibility.