CSS Syntax Validator
Check CSS syntax, find errors by line and column, and explore a structured tree without applying the styles to your page.
How do I find syntax mistakes in CSS?
Paste your stylesheet and select Check syntax. The parser reports syntax problems with line and column numbers. Expand the parsed structure and download its JSON tree. Syntax checks do not prove that a browser supports every property or value.
Your result
A little clarity, right here.
Start with your own content or load the example. Your result will appear here.
Three simple steps
How to use CSS Syntax Validator
Paste your source or open a text file. Try the example if you are learning.
Choose the options and run the tool. Your source stays on this device.
Review the result, then copy it or download the files.
Common questions
Good to know
Understand the result.
Keep the original.
Is this tool free, and are my files uploaded?
This tool is free with no account required. The work happens in your browser. Your input and files are not sent to a processing server.
What are the limits and details?
Up to 100,000 UTF-8 bytes, 5,000 CSS statements and 40 nesting levels. Processing stops after 30 seconds. Files stay on your device. CSS is never applied to this page and JavaScript is never executed. Uses CSS Tree for syntax parsing and PostCSS for block structure. It does not validate every property value, check accessibility, or test browser support. A parser may stop at the first fatal error.
100 KB of source. Local processing. Cancel at any time.