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W3C Markup Validation Service vs HTMLHint: catalog facts
W3C Markup Validation Service	HTMLHint
Free A free service run by the W3C.	Free Free and open source, supported through Open Collective.
Web	Windows, macOS, Linux, Command line
Validate by URL, file upload or direct input Choice of character encoding and document type	Rules can be switched on, off or customised per project Runs from the command line or in a build pipeline
HTML5 validation is marked experimental Modern HTML is better served by the separate Nu Html Checker	Checks HTML only, not CSS or JavaScript Needs Node.js and npm for the command-line version
Web application	Downloadable app
Closed source	Open source
License not stated	License: MIT
No account needed	No account needed
Needs internet	Works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked October 2, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.