validator.w3.org
non-DTD-based Validator
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Find Broken Links
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Contribute
Contribute - The W3C Markup Validation Service
About
About this service. The Markup Validator is a free service by W3C that helps check the validity of Web documents.. Most Web documents are written using markup languages, such as HTML or XHTML.These languages are defined by technical specifications, which usually include a machine-readable formal grammar (and vocabulary). ). The act of checking a document against these constraints is called ...
Docs
Docs - The W3C Markup Validation Service
Feedback
Feedback - The W3C Markup Validation Service