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W3C Markup Validation Service vs SuperHTML: catalog facts
W3C Markup Validation Service	SuperHTML
Free A free service run by the W3C.	Free Free and open source under the MIT licence.
Web	Windows, Command line
Validate by URL, file upload or direct input Choice of character encoding and document type	Validation and formatting in one tool Works as a language server in editors
HTML5 validation is marked experimental Modern HTML is better served by the separate Nu Html Checker	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.