Validation Tools

What tools are people using to validate their web pages? In Refactoring HTML so far I’m writing about four, somewhat related tools:

Anything else worthy of mention? In particular, is there anything significantly different enough from these four that it deserves to be called out separately? Or is there anything better that should replace one of these options? (This is a relatively small book, and I am trying very hard not to cover absolutely every possibility and option.) Open source tools are strongly preferred.

2 Responses to “Validation Tools”

  1. Stefan Tilkov Says:

    nXML mode?

  2. Craven Says:

    I like HTMLValidator. (

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