Free Online CSS Validator

Paste CSS below to check for unbalanced braces, unclosed comments, and malformed declarations. Runs entirely in your browser.

How to validate CSS online

  1. 1

    Paste your CSS

    Copy in the stylesheet or rule block you want to check.

  2. 2

    Click "Validate"

    The tool scans for brace balance, unclosed comments, and malformed declarations.

  3. 3

    Read the result

    A green checkmark means no structural issues were found. Otherwise, each issue explains what looks wrong and where.

  4. 4

    Fix and re-check

    Correct the flagged issue and validate again until you get a clean pass.

Example use cases

1

Debugging styles that won't apply

Find the missing brace or colon that's silently breaking a whole block of rules.

2

Reviewing generated CSS

Check CSS produced by a preprocessor, template, or design tool for structural mistakes before committing it.

3

Checking a pasted snippet

Quickly verify a CSS block copied from a chat or ticket doesn't have an obvious syntax error.

Frequently asked questions

What does this CSS validator check?

It checks for unbalanced braces and parentheses, an unclosed comment, a stray closing brace with no matching opener, and declarations inside a rule that are missing the colon between property and value.

Is this a full W3C CSS validator?

No. This checks structural syntax only — it doesn't check that property names or values are valid CSS, or catch vendor-prefix and browser-compatibility issues the way the W3C CSS Validator does.

Will it flag braces inside a string or URL?

No. Quoted strings and url(...) values are skipped before the brace count runs, so characters inside them are never mistaken for structural punctuation.

Is my CSS uploaded anywhere?

No. Validation runs entirely in your browser using JavaScript — nothing you paste is sent to a server.