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Nu Html Checker vs SuperHTML: catalog facts
Nu Html Checker	SuperHTML
Free Free to use on the W3C website.	Free Free and open source under the MIT licence.
Web	Windows, Command line
Checks against current HTML conformance rules rather than old doctypes Accepts a URL, a file upload or pasted markup	Validation and formatting in one tool Works as a language server in editors
Checks one document at a time Behavior is described as experimental and subject to change	Focused on HTML only No formal releases listed on the repository
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.