HTML Validator is a Mozilla extension that adds HTML validation inside Firefox and Mozilla. The number of errors of a HTML page is seen on the form of an icon in the status bar when browsing. The details of the errors are seen when looking the HTML source of the page.

The extension is based on Tidy and OpenSP. Both algorithms were originally developed by the Web Consortium W3C. Both algorithms are embedded inside Mozilla/Firefox, which means the validation can be done locally on your machine.

• 1. Browser Integration:
  • No need to visit an external site, as HTML validation is performed while viewing the page. A handy icon in the status bar reveals any validation errors.
  • If the page contains HTML frames or iframes, you can see the validation result of the main page as well as any frames.
• 2. Source View:
  • Details regarding any validation errors can be seen when viewing the source of the page.
  • In most cases, additional info on how to fix errors is displayed! Great not only for cleaning up your html page, but also educational to avoid similar errors in the future.