CSS Validator

About This Tool

The CSS Validator checks your CSS code for common syntax errors including unmatched braces, missing semicolons, malformed declarations, and empty rule sets. Paste your stylesheet and instantly see a list of issues with line numbers so you can fix them quickly.

All validation runs in your browser — no CSS is sent to any server. The validator covers the most common structural errors. For full W3C specification compliance, use the official W3C CSS Validation Service.

How to Use

1. Paste your CSS code into the input area, or click Sample (Valid) or Sample (Errors) to load an example.
2. Click Validate to run the validation check.
3. Review the results — errors are shown in red with line numbers, warnings in amber.
4. Fix the issues in your CSS editor and re-validate until no errors remain.

Use Cases

Front-end developers debug styles that are not applying correctly — often caused by a missing semicolon silently invalidating subsequent declarations. Designers pasting CSS from design tools validate it before embedding in a project. Students learning CSS catch syntax mistakes early without needing browser DevTools.

FAQ

• Does this validate CSS properties against the W3C spec? — No. This tool checks structural syntax (braces, semicolons, colons). For full property validation, use the W3C CSS Validation Service.
• Why does my valid CSS show a warning? — The validator uses heuristics and may flag edge cases like single-line rules or non-standard at-rules. Warnings are informational — they do not necessarily indicate a bug.
• Does it support CSS variables and custom properties? — Yes. Lines containing --variable-name are recognized as custom property declarations.
• Is my CSS sent to a server? — No. Validation runs entirely in your browser using JavaScript. Your code never leaves your device.