W3C Markup Validation Service vs Nu Html Checker: catalog facts
 W3C Markup Validation Service |  Nu Html Checker |
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Free A free service run by the W3C. |
Free Free to use on the W3C website. |
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Web |
Web |
- Validate by URL, file upload or direct input
- Choice of character encoding and document type
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- Checks against current HTML conformance rules rather than old doctypes
- Accepts a URL, a file upload or pasted markup
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- HTML5 validation is marked experimental
- Modern HTML is better served by the separate Nu Html Checker
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- Checks one document at a time
- Behavior is described as experimental and subject to change
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Web application |
Web application |
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Closed source |
Closed source |
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License not stated |
License not stated |
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No account needed |
No account needed |
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Needs internet |
Needs internet |
Checked September 23, 2026 | Checked September 23, 2026 |
Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.
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