Spot CSS mistakes instantly
Paste your stylesheet and every rule is checked for syntax errors, unknown properties (like colr) and values that aren't valid for their property — each with its line number and the code shown for context.
Validation uses the CSS specifications built into css-tree, so it understands modern CSS: grid, flexbox, custom properties, calc(), clamp(), container queries and new color functions. Vendor-prefixed properties are noted but not treated as errors, and everything runs in your browser.
How to validate CSS
- 1
Paste your CSS
A snippet or a whole stylesheet.
- 2
Click Validate
Results appear instantly.
- 3
Fix the listed lines
Errors first.
Key features
Syntax and value checks
Not just parsing.
Modern CSS support
Grid, variables and more.
Line numbers
With the code line shown.
Private
Nothing is uploaded.
Common uses
- Debugging styles: Find why a rule is ignored.
- Code reviews: Catch typos before merging.
- Learning CSS: See which values are allowed.
Tips and good to know
- Browsers silently ignore invalid declarations, which is why a single typo can make a style “not work”.
- Format messy CSS first with the CSS Formatter.
Frequently asked questions
Does it support CSS variables?
Yes. Custom properties (--name) are accepted, since their values can be anything.
Is this the W3C CSS validator?
It uses a different engine (css-tree) built on the same specifications, runs in your browser and understands newer CSS features.
Are vendor prefixes errors?
No. They're flagged as informational so you can check whether they're still needed.