Nu HTML Checker (W3C)
by validator.github.io
Data validators
Added on October 31st, 2026
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What it does
The Nu HTML Checker is the validator behind validator.w3.org/nu. Send it an HTML, CSS or SVG document, or a URL to check, and get back the errors and warnings in JSON, XML or text, with line and column numbers. Useful for automated quality checks in build pipelines. Free and open source; for heavy use, run your own copy of the checker.
More information: https://validator.github.io/validator/
