HTML validator extension

The HTML validator extension for Mozilla and Firefox validates web pages on the fly. The extension is based on Tidy, works without accessing the W3C validator (or any other server), and displays helpful messages that explain any errors or warnings.

Posted on March 14, 2005 in Quicklinks, Web Standards


  1. I’m not sure if this thing is working properly. My website didn’t pass the test but that’s possible for I don’t know much about html (for as long as I can’t “type” a whole webpage) but I know people who do. And their pages don’t pass the test as well… Or am I wrong? (which is pretty possible?)

  2. Wannes: Your website doesn’t validate. See Here:

  3. Have you noticed how the AdSense code is killing our validation? Sigh….

  4. One question, how accurate is Tidy thru the years? Compared to the ol’ W3C validator.

  5. March 15, 2005 by Roger Johansson (Author comment)

    Wannes: I think it’s working properly.

    Simon: Yeah :(

    KevinN: I don’t think there is any difference in accuracy between Tidy and the W3C validator.

  6. Well, as a I noticed, I don’t know much about html. And I found out my website doesn’t validate at all: but there are more of them which don’t validate… No excuses, I know, but when I ask Tidy to clean it all up, the little plug-in gives more warnings every time I’m asking him… So far so good, ‘cause I’m sure that it won’t be the main purpose of it all: to clean up my messy pages…

  7. I was under the impression Tidy was originally a “Lint Checker” rather than a true Validator; I assume that is still the case. Since Genuine HTML validators employ SGML parsers to check a document’s syntax against a DTD.

  8. March 15, 2005 by Marc

    Tidy is a linter adn has a lot of advantages. Because SGML or DTD validation has a lot of shortcomings.

    Mostly that a DTD does not allow to specify the attributes values. As a result, W3C validator does not check attributes values in HTML tags. This is the main reason why tidy gives more errors than W3C validator.

    If you have question about tidy result, there is a mailing list:

    Also, no additional tests are possible (like accessibility). Tidy implements the 3 levels of accessibility of WAI:

  9. Thanks Marc, I regularly use both types of tools for the said reason at least it now clears it up. :)

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