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W3C Markup Validation Service vs Rocket Validator: catalog facts
W3C Markup Validation Service	Rocket Validator
Free A free service run by the W3C.	Paid Paid subscription service with a free trial.
Web	Web
Validate by URL, file upload or direct input Choice of character encoding and document type	Site-wide HTML and accessibility checks in one report Up to 5,000 pages per report
HTML5 validation is marked experimental Modern HTML is better served by the separate Nu Html Checker	Paid service after the trial Requires an account
Web application	Hosted service
Closed source	Closed source
License not stated	License not stated
No account needed	Account needed
Needs internet	Needs internet
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked September 23, 2026

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