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AChecker vs Nu Html Checker: catalog facts
AChecker	Nu Html Checker
Free Single checks are free; automatic monitoring is a paid ACHECKS subscription.	Free Free to use on the W3C website.
Web	Web
Checks by URL, file upload or pasted HTML Choice of several guideline sets and levels	Checks against current HTML conformance rules rather than old doctypes Accepts a URL, a file upload or pasted markup
Guidelines stop at WCAG 2.0 Older interface with limited explanation of fixes	Checks one document at a time Behavior is described as experimental and subject to change
Web application	Web application
Closed source	Closed source
License not stated	License not stated
No account needed	No 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.