CSS Validator
Validate your CSS code for syntax errors
Input CSS
Validation Result
What is a CSS Validator?
Broken CSS can silently ruin your website's design. A CSS validator checks your CSS (Cascading Style Sheets) for syntax errors, invalid properties, and potential problems before they cause issues in production. This tool catches mistakes like missing semicolons, typos in property names, or incorrect values that browsers might ignore.
According to MDN Web Docs, valid CSS ensures consistent rendering across browsers. Our validator follows the official CSS specifications from W3C, catching errors that could cause unexpected layout issues. The W3C CSS Validation Service is the gold standard, and our tool provides quick validation right in your browser.
All validation happens locally. Your CSS stays private – no server uploads required.
Why Validate Your CSS
Catch Syntax Errors
Find missing semicolons, unclosed brackets, or invalid selectors before deployment. One typo can break your entire stylesheet – validation catches these instantly.
Check Property Names
Typed "colour" instead of "color"? Or "font-wieght" instead of "font-weight"? The validator catches misspelled properties that browsers would silently ignore.
Verify Values
Make sure color codes are valid, units are correct, and values match their properties. Prevents weird rendering bugs caused by invalid value formats.
Real-time Feedback
See validation results as you type. Error messages point to exact problems with line numbers, making fixes quick and easy.
File Upload Support
Validate entire CSS files without copy-pasting. Upload any .css file and get instant validation feedback on the whole stylesheet.
Syntax Highlighting
Code editor with syntax highlighting makes errors easier to spot visually. See your CSS properly formatted while validation runs.
How to Validate CSS
Add Your CSS
Paste your CSS into the left editor, or upload a .css file. Click "Sample" to see example validation. The tool accepts any CSS – from simple selectors to complex media queries.
Automatic Validation
Your CSS is validated instantly. The tool checks syntax, property names, values, and structure. Valid CSS shows a success badge. Errors appear with descriptions and line numbers.
Fix Errors
Error messages tell you exactly what's wrong and where. Fix the issues in the editor and watch validation update in real-time. Once everything's valid, your CSS is ready to use.
When to Validate CSS
Before Deployment
Always validate before pushing to production. Catching errors early prevents broken layouts, weird styling issues, and emergency hotfixes. Takes seconds, saves hours of debugging.
Debugging Layout Issues
Styles not applying? Colors wrong? Validation might reveal the issue. A single syntax error can break an entire stylesheet – find it fast with validation.
Learning CSS
New to CSS? Validation teaches you correct syntax. Error messages explain what's wrong, helping you learn proper CSS structure and avoid common mistakes.
Code Reviews
Validate CSS before submitting pull requests. Valid code means fewer review comments and faster approvals. Shows attention to detail and code quality.
Common Questions
What errors does this catch?
Syntax errors (missing brackets, semicolons), invalid property names, incorrect values, malformed selectors, and unclosed strings. Basically anything that violates CSS syntax rules.
Does valid CSS mean perfect CSS?
No. Validation checks syntax, not quality. Your CSS can be syntactically valid but poorly organized, inefficient, or using bad practices. For best practices, check guides like web.dev's CSS course.
What about vendor prefixes?
Vendor prefixes like -webkit-, -moz-, and -ms- are technically non-standard but widely used. Most validators flag them as warnings, not errors. They're fine to use when needed for browser compatibility.
Can I validate SCSS or SASS?
This validates standard CSS. For Sass/SCSS, first compile to CSS (using our SCSS to CSS converter), then validate the compiled CSS.
Why do browsers accept invalid CSS?
Browsers follow error recovery rules to handle mistakes gracefully. They skip invalid declarations and continue parsing. This means invalid CSS might "work" but unpredictably. Always validate to ensure consistent behavior.
Is this as thorough as W3C's validator?
For most common cases, yes. For comprehensive validation including CSS3 modules and edge cases, the official W3C validator is more thorough. This tool provides quick, convenient validation for everyday use.
Related CSS Tools
Validation is important, but you might also need these:
Want to learn more about CSS? Check the official W3C CSS learning resources or browse CSS-Tricks for practical guides.