When a style does nothing, the reason is often a tiny typo the browser silently ignores. This checker reads your CSS with the browser’s own CSS engine and points to unknown properties (suggesting the right spelling), values the property does not accept, broken selectors, missing semicolons and braces, empty rules and properties set twice.
loading toolHow to use the css checker
- Paste your code into the box (or tap Try a sample).
- Read the list of problems: ✕ marks an error, ! a warning.
- Tap Show next to a problem to jump to that line, fix it, and watch the list update.
Good to know
- A missing semicolon makes the browser drop the next line too, so fix those first.
- If a property is set twice in one rule, the later one wins.
Questions
Why does it say a new property is unknown?
It checks against the CSS your own browser understands. A very new property may be missing in an older browser, which is useful to know before you rely on it.
Does it understand media queries, nesting and custom properties?
Yes: @media, @supports, @container, @layer, @keyframes, @font-face, CSS nesting with & and --custom-properties with var() are all understood.
Are vendor prefixes errors?
No. Properties like -webkit-line-clamp are skipped, because they are meant for other browsers.
Is my data private?
Yes. Everything happens inside your own browser: nothing you type or choose is uploaded to us or anyone else.
Is it free?
Completely free, with no sign-up, no watermark and no limit on how many times you use it. Light ads keep the site running.
