HTMLValidator is a tool that allows you to verify that your webpages meet W3C html and xhtml standards.
Because HTMLValidator uses the same validation technique as the official validator you can be assured the the pages you create work correctly.
HTMLValidator works without access to the web.
This means that you don't need an active internet connection to validate pages and the validation occurs entirely on your own machine. Your pages remain secure and you don't need to open your firewall to validate your intranet.
HTMLValidator can validate as many pages as you like, as many times as you like.
Plus you can keep a set of pages in HTMLValidator and revalidate them every time you make a change.
HTMLValidator supports both local files and pages from a web server
HTMLValidator also supports direct validation from Safari.
It can actually validate the page that you see in Safari including any login or cookie driven content and it does this by grabbing the source from Safari, not by downloading the page again. This means that you validate dynamic content as easily as static content and be certain that even highly complicate pages are correct.