HTML Validator
Check HTML for unclosed tags, mismatched nesting, duplicate IDs, and missing attributes.
7 errors, 1 warning
errorline 9, col 3
Unclosed tag <p>
<p>This is a paragraph with an <a href="https://example.co
warningline 10, col 3
<img> missing recommended "alt" attribute
<img src="photo.jpg">
errorline 12, col 5
Unclosed tag <span>
<span>Nested content</div>
errorline 12, col 25
Mismatched tag: expected </span> (opened at line 12), found </div>
<span>Nested content</div>
errorline 13, col 3
Closing tag </div> has no matching open tag
</div>
errorline 14, col 3
Unclosed tag <p>
<p>Another paragraph
errorline 15, col 1
Mismatched tag: expected </p> (opened at line 14), found </body>
</body>
errorline 16, col 1
Mismatched tag: expected </p> (opened at line 14), found </html>
</html>
HTML validation and best practices
Valid HTML improves accessibility, search engine indexing, and cross-browser compatibility. This validator checks for structural issues: unclosed tags, mismatched nesting, duplicate IDs, and missing required attributes like alt on images. For full W3C validation, use the official Nu HTML Checker at validator.w3.org.
Private & free — this tool runs entirely in your browser.
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