HTML Validator

Your data never leaves your browser

Check your HTML for common issues and missing declarations.

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About HTML Validator

Validate your HTML markup by parsing it with the browser's DOMParser and checking for parse errors, missing DOCTYPE declarations, and other structural issues. Get instant feedback on whether your HTML is valid.

How to use

  1. Paste your HTML into the input panel.
  2. The validator checks for common issues and shows a pass or fail result.
  3. Review any reported issues and fix them in your source HTML.

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Frequently Asked Questions

FAQs about HTML Validator

What does the validator check?

It checks for parse errors, a missing <!DOCTYPE html> declaration, and structural issues detected by the browser's DOMParser.

Is this a W3C-standard validator?

No. This is a browser-based quick check. For full W3C compliance validation, use the official W3C Markup Validation Service.

Why might valid HTML still show issues?

This validator flags missing DOCTYPE and parser errors. Some technically valid HTML patterns may still trigger warnings.

What is a DOCTYPE declaration?

<!DOCTYPE html> tells browsers this is an HTML5 document. Without it, browsers may render in quirks mode, causing layout inconsistencies.

Is my data safe?

Yes. All validation happens in your browser. No data is sent to any server.