Validate by URI

Validate a document online:

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Validate by File Upload

Upload a document for validation:

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Note: file upload may not work with Internet Explorer on some versions of Windows XP Service Pack 2, see our information page on the W3C QA Website.

Validate by direct input


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Use Doctype:

This validator checks the markup validity of Web documents in HTML, XHTML, SMIL, MathML, etc. If you wish to validate specific content such as RSS/Atom feeds or CSS stylesheets, MobileOK content, or to find broken links, there are other validators and tools available.

Important This instance of the validator is either a development version used for testing purposes, or a local copy of the W3C Markup Validator software used for development and testing purposes.
The official validation service supported by the W3C is at