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

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