A CSS validator checks your stylesheets for syntax errors, unbalanced braces, and structural issues using the browser's native CSSOM API — the same parser that renders your pages. Paste CSS below to get an instant VALID/INVALID verdict with error details, rule counts, and syntax highlighting.
Errors
Warnings
Parsed Rules
CSS Syntax Reference
Basic rule structure:
selector {
property: value;
property: value;
}
Common @rules:
@media— responsive breakpoints@keyframes— animations@import— import stylesheets@font-face— custom fonts@supports— feature queries
How to Use the CSS Validator
This CSS validator uses your browser's own CSS parser — the same engine that renders websites — to check stylesheets for syntax errors and structural issues. Results are instant and match what real browsers will actually accept.
Step 1: Paste Your CSS
Copy your CSS from your text editor, browser DevTools, or any stylesheet source and paste it into the textarea. The tool accepts any valid CSS including media queries, keyframe animations, custom properties (CSS variables), and pseudo-selectors.
Step 2: Validate
Click "Validate CSS" to run the check. Results show an overall VALID or INVALID badge, followed by statistics on rule count, selectors, properties used, and @rules found. Any errors are listed with descriptions to help you locate and fix them.
Understanding CSSOM Validation
Modern browsers use the CSSOM (CSS Object Model) to parse CSS. Invalid properties are silently ignored rather than throwing parse errors — this is by design and matches the CSS error handling specification. The validator supplements browser parsing with custom structural checks for common issues like unbalanced braces and empty selectors.
Common CSS Errors
The most common issues are unbalanced curly braces (a missing }), missing semicolons between declarations, invalid values for known properties, and typos in selector syntax. Run this CSS validator as part of your development workflow before pushing changes to catch issues early.
FAQ
How does this CSS validator work?
This tool uses the browser's native CSSOM (CSS Object Model) API to parse your CSS. It injects a temporary style element, reads the parsed rules, and reports any errors detected by the browser's built-in CSS parser — the same engine that renders websites.
What errors can this CSS validator detect?
The validator checks for syntax errors, unbalanced braces, invalid property values, malformed selectors, and structural issues. It also performs custom checks for balanced braces, empty selectors, and common @rules.
Is my CSS code sent to a server?
No. All validation runs locally in your browser using the built-in CSSOM API. Your CSS is never sent to any server — it's processed entirely client-side.
Does this validator check all CSS properties?
The browser's CSSOM API silently ignores unknown properties rather than throwing errors, which matches real-world browser behavior. Valid CSS according to this tool will work in modern browsers. Vendor-prefixed properties may or may not be recognized depending on your browser.
Is this tool free?
Yes, completely free. Paste your CSS and get instant validation results. No account or signup required.
What is a CSS @rule?
CSS @rules are special directives like @media (responsive breakpoints), @keyframes (animations), @import (import stylesheets), @font-face (custom fonts), and @supports (feature queries). The validator counts and reports these rules separately.