HTML Validator
Check HTML structure: unclosed tags, nesting errors, and invalid attributes.
About the HTML Validator
Validate HTML structure entirely in your browser: unclosed or improperly nested tags, invalid attributes, disallowed parent-child relationships, and duplicate identifiers. The checker understands void elements and the HTML5 content model, and distinguishes errors from warnings so you can prioritize fixes.
Frequently asked questions
Does this replace the W3C validator?
No — the W3C validator checks against the full specification, including doctype, encoding, and accessibility rules. This tool focuses on structural problems like unclosed tags and bad nesting, and runs instantly with no upload.
What is the difference between an error and a warning?
Errors are definite problems (unclosed tags, invalid nesting). Warnings are likely problems that may still be intentional (unknown elements, duplicate attributes).