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CSS Validator

Validators

Validate CSS code for syntax errors and compliance with W3C standards.

⚡ Instant🔒 Private, in your browser🆓 Free, no sign-up👥 For developers
Your data never leaves your browser. We do not store inputs.

What CSS Validator does

The CSS Validator parses your stylesheet and flags the errors that make browsers silently drop rules: unclosed braces and comments, missing semicolons and colons, unknown properties, invalid values, malformed selectors and invalid media queries. Paste a full stylesheet or a snippet and get a line-by-line report. Structure is parsed by the tool and values are checked with your browser's own CSS engine, all locally in your browser.

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Reviewed by the FreeToolsVerse team · Last updated · How we check our tools

How to use CSS Validator

  1. Paste your CSS code into the editor
  2. Click Validate
  3. Review the list of errors with line numbers
  4. Fix the flagged lines and re-validate until it comes back clean

Who should use it

Made for developers. Typical uses:

  • Catching a missing semicolon or unclosed brace that's silently breaking a stylesheet
  • Checking a third-party or copied CSS snippet before adding it to a production site
  • Confirming custom CSS pasted into a CMS theme editor is spec-compliant before saving

Frequently asked questions

Is it free to use?
Yes, completely free.
Is my CSS uploaded to a server?
No, validation happens entirely in your browser.
Does it check browser compatibility, not just syntax?
Partly. Braces, strings, comments and at-rule structure are parsed by the tool itself, while property names, values, selectors and media queries are checked with your browser's own CSS engine. Anything your current browser does not support, such as a very new property, is flagged, so running the check in an up-to-date browser gives the most accurate result.
Why does my CSS render fine in the browser but still fail validation?
Browsers silently drop any declaration they cannot parse and carry on, so a page can look mostly fine while some of your rules are being ignored. The validator shows you exactly which lines are being thrown away.
Can I validate a single rule instead of a whole file?
Yes, though pasting the full stylesheet gives more accurate results since some errors depend on surrounding context.

Learning resources

Explore more in Validators, read the guides and articles, or see how we test our tools.

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