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HTML-validate vs W3C Markup Validation Service: catalog facts
HTML-validate	W3C Markup Validation Service
Free Free to use, with the source code published on GitLab.	Free A free service run by the W3C.
Command line	Web
Validates entirely offline, so no markup is uploaded Handles HTML fragments inside Vue.js and AngularJS components	Validate by URL, file upload or direct input Choice of character encoding and document type
Command-line and tooling oriented, with no graphical interface Checks markup only, not CSS or accessibility in a browser	HTML5 validation is marked experimental Modern HTML is better served by the separate Nu Html Checker
Downloadable app	Web application
Closed source	Closed source
License not stated	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.