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.
How to Use the CSS Validator
Follow these steps to validate your CSS. Each step uses the actual buttons and panels on this page.
Paste, Upload, or Load Sample
Paste CSS into the left editor, or click Upload to load a file. Click Sample to see example telecomm subscriber dashboard styles. Example:
.subscriber-card {
border: 1px solid #e0e0e0;
padding: 16px;
border-radius: 8px;
}
.plan-badge {
display: inline-block;
padding: 4px 8px;
background: #e3f2fd;
}View Validation Result
The right panel shows the result: success badge for valid, error details for invalid. Checks syntax, property names, values, and structure. Errors include line numbers.
Fix Errors
Use error messages to fix missing semicolons, unclosed brackets, or invalid properties. Validation updates in real-time. All processing runs in your browser.
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 per MDN vendor prefix documentation. Most validators flag them as warnings, not errors. They're fine for CSS 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: