What is CSS Validator?
CSS Validator is a free online tool that checks your CSS code for syntax errors, best practices, and potential issues. Whether you're writing inline styles or large stylesheets, this tool helps ensure your CSS is valid and follows modern standards.
Our validator checks for common mistakes like syntax errors, missing semicolons, unbalanced braces, and provides warnings about best practices like vendor prefixes and specificity issues.
Why Use CSS Validator?
- Syntax Checking — Find syntax errors before they cause problems
- Best Practices — Get recommendations for better CSS
- Vendor Prefixes — Ensure cross-browser compatibility
- Specificity Analysis — Avoid overly specific selectors
- Format Output — Beautify and minify CSS
- Browser Compatibility — Write CSS that works everywhere
Common CSS Errors
| Error | Description |
|---|---|
| Unbalanced Braces | Mismatched { and } characters |
| Missing Semicolons | Declarations not properly terminated |
| Invalid Property Names | Properties starting with numbers |
| Invalid Values | Values not matching property requirements |
| Unknown Properties | Misspelled or invalid CSS properties |
| Duplicate Properties | Same property defined multiple times |
CSS Best Practices
- Use Vendor Prefixes — Add -webkit-, -moz- prefixes for experimental properties
- Keep Specificity Low — Avoid deeply nested selectors
- Use Shorthand Properties — margin: 10px instead of individual properties
- Group Related Styles — Keep related rules together
- Use CSS Variables — For reusable values
- Minify for Production — Reduce file size for faster loading
Vendor Prefixes Guide
Some CSS properties require vendor prefixes for older browsers:
| Property | Prefixes |
|---|---|
| transform | -webkit-, -moz-, -ms-, -o- |
| border-radius | -webkit- |
| box-shadow | -webkit- |
| flex | -webkit- |
| grid | -ms- |
| animation | -webkit-, -moz- |
CSS Specificity
Understanding specificity helps avoid CSS conflicts:
- Inline styles: 1000 points
- IDs: 100 points
- Classes, attributes, pseudo-classes: 10 points
- Elements, pseudo-elements: 1 point
Frequently Asked Questions
What's the difference between CSS validation and linting?
CSS validation checks if your code conforms to the official CSS specification. Linting goes further by checking for best practices, potential bugs, and coding style issues.
Can I validate CSS from a URL?
Currently, you can paste CSS directly. For external stylesheets, you can copy the CSS content and paste it here for validation.
How do I minify CSS?
Click "Minify CSS" in the Quick Actions section. This removes whitespace and comments to reduce file size for production use.
Does this tool check browser compatibility?
The tool provides warnings about vendor prefixes and common compatibility issues. For detailed browser support, check Can I Use or MDN.