Find syntax errors, misspelled properties and invalid values in your CSS.
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The validator uses CSSTree, which knows the grammar of every standard CSS property. It reports syntax errors, unknown properties such as a misspelled colr, and values that a property doesn't accept, such as width: 10pz or an empty color. Each problem is listed with its line and column so you can fix it quickly.
Catch misspelled property names and units that browsers silently ignore.
Check a stylesheet you edited by hand.
See exactly which values a property accepts.
CSS syntax, whether each property name exists in the CSS specifications, and whether each value is allowed for its property. Each problem is listed with its line and column.
Browsers silently ignore declarations they don't understand, so a typo just doesn't apply. The validator reports it so you know the style isn't working.
No. It checks your CSS against the specifications; whether a browser supports a feature is a separate question.
Yes. Custom properties (--name), var(), calc(), grid, and newer at-rules are part of the grammar it uses.
No. Everything runs in your browser; nothing you paste or upload is sent to our servers.