Validate HTML syntax instantly with our free online HTML validator. Check for unclosed tags, malformed attributes, nesting errors, and ensure your markup is valid. 100% client-side.
Our HTML Validator tool helps you check the syntax and structure of your HTML code instantly. It detects common errors such as unclosed tags, mismatched opening and closing tags, invalid attribute syntax, missing required attributes, and improper nesting. All processing happens in your browser — your code never leaves your device.
This tool validates HTML structure using a comprehensive parser that checks for common syntax errors, unclosed tags, mismatched tags, and malformed attributes. While it catches most structural mistakes, it does not perform full W3C HTML specification compliance checking like the official W3C validator.
Absolutely. All validation happens entirely in your browser. No HTML code is sent to any server.
Yes! Simply copy and paste the contents of your HTML file into the input area, then click Validate. You can also paste multiple HTML files at once.