Validate CSS

Check CSS for malformed blocks, declarations, at-rules, and known property issues.

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ToolCSS Validator
Input
Output
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Preview

How it works

Stylesheet text is tokenized and checked for balanced blocks, valid declarations, known property-value grammar, and malformed at-rules. Findings are reported without applying styles.

  • Syntax errors are separated from unknown-property warnings.
  • Vendor extensions can remain intentional.

Worked example

Catch missing colon in declaration
Detect a missing colon in a CSS property declaration
Input
											.btn {
  color: blue;
  font-size: 14px;
}
.card {
  padding 10px;
}
Output
												Found 1 error(s)

Stats: 2 rules, 2 selectors, 2 properties

Errors:
  - Invalid declaration: "padding 10px" (missing colon)

When to use this

CI, editors, and distributed design-system packages validate CSS.

Edge cases

  • Custom properties may contain unusual tokens.
  • A missing semicolon before a closing brace can still parse the final declaration.
  • Vendor prefixes are not automatically errors.

References