CSS Validator & Autoprefixer
Validate CSS against the specifications — syntax errors, unknown properties, invalid values, duplicates, unclosed blocks — and add vendor prefixes for your target browsers with Autoprefixer.
How to use
- 1Paste your CSS.
- 2Fix the listed errors and warnings (each has a line number).
- 3Choose target browsers and add vendor prefixes.
Frequently asked questions
Does it support modern CSS?
Yes — grid, custom properties, container queries, :has() and other current features are recognized.
Why isn't a value with var() checked?
The value of a custom property is only known when the page renders, so values containing var() are skipped.
Do I still need vendor prefixes?
Only for a few properties (e.g. user-select, some mask and backdrop features). Autoprefixer adds just the ones your chosen browsers need.