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Nu Html Checker vs HTMLHint: catalog facts
Nu Html Checker	HTMLHint
Free Free to use on the W3C website.	Free Free and open source, supported through Open Collective.
Web	Windows, macOS, Linux, Command line
Checks against current HTML conformance rules rather than old doctypes Accepts a URL, a file upload or pasted markup	Rules can be switched on, off or customised per project Runs from the command line or in a build pipeline
Checks one document at a time Behavior is described as experimental and subject to change	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.