CSS Validator

What is CSS Validator Tool?

CSS Validator is a comprehensive web-based tool that validates your CSS code against W3C (World Wide Web Consortium) standards and specifications. This online validator checks for syntax errors, compliance issues, and potential problems that could affect your website's styling and cross-browser compatibility. Built using the official W3C CSS validation service, it ensures your stylesheets meet international web standards.

In modern web development, CSS validation is essential for creating robust, maintainable, and cross-browser compatible websites. Our validator provides real-time feedback on CSS syntax, property usage, and compliance with various CSS profiles including CSS1, CSS2, CSS2.1, CSS3, and specialized profiles for mobile devices and SVG graphics.

The tool supports multiple validation methods including direct CSS input, URL validation for live websites, and file upload for local CSS files. Whether you're a beginner learning CSS or an experienced developer ensuring code quality, this validator helps maintain professional standards and prevents styling issues across different browsers and devices.

Core Features of CSS Checker

Our CSS validator offers comprehensive validation capabilities designed to ensure your stylesheets meet professional standards:

• W3C Standards Compliance: Validates against official W3C CSS specifications ensuring your code follows international web standards
• Multiple CSS Profiles: Supports CSS1, CSS2, CSS2.1, CSS3, CSS3+SVG, SVG, Mobile, ATSC-TV, and TV profiles for different use cases
• Syntax Error Detection: Identifies CSS syntax errors, malformed rules, missing semicolons, and invalid property values
• Property Validation: Checks CSS properties against the selected profile to ensure compatibility and proper usage
• Warning System: Configurable warning levels (0-3) to catch potential issues and deprecated properties
• Multiple Input Methods: Validate by direct input, URL/URI, or file upload with support for .css files
• Real-time Feedback: Instant validation results with detailed error messages and line-by-line analysis
• Media Type Support: Validate CSS for different media types including screen, print, mobile, TV, and accessibility devices
• Error Highlighting: Visual indicators in the code editor showing exact locations of issues with detailed explanations
• Severity Classification: Distinguishes between critical errors and warnings for better issue prioritization

Why Use CSS Code Validator?

CSS validation provides numerous benefits for web developers and designers:

• Cross-Browser Compatibility: Ensure your CSS works consistently across all major browsers and devices
• Standards Compliance: Follow W3C standards for better accessibility, SEO, and future-proofing
• Error Prevention: Catch syntax errors and invalid properties before they cause styling issues
• Performance Optimization: Identify inefficient CSS patterns and deprecated properties that could impact performance
• Maintainability: Clean, valid CSS is easier to maintain, debug, and extend over time
• Professional Quality: Ensure your stylesheets meet industry standards and best practices
• Learning Tool: Educational feedback helps developers understand CSS specifications and improve their skills
• Accessibility Compliance: Valid CSS contributes to better accessibility and screen reader compatibility
• SEO Benefits: Clean, valid code can positively impact search engine rankings
• Team Consistency: Ensure all team members follow the same CSS coding standards

CSS Validation Profiles

Our validator supports multiple CSS profiles to match your specific requirements:

CSS Code Validation Example

Here are examples of common CSS issues the validator can detect:

/* Missing semicolon */
body {
  font-family: Arial, sans-serif
  margin: 0;
}

/* Invalid property value */
.container {
  display: flexbox; /* Should be 'flex' */
  width: 100%;
}

/* Syntax error - missing closing brace */
.header {
  color: #333;
  font-size: 2em
/* Missing closing brace */

/* Invalid color value */
.button {
  background-color: #xyz; /* Invalid hex color */
  border: 1px solid;
}

/* Proper syntax with semicolons */
body {
  font-family: Arial, sans-serif;
  margin: 0;
}

/* Correct property values */
.container {
  display: flex;
  width: 100%;
}

/* Complete rule with closing brace */
.header {
  color: #333;
  font-size: 2em;
}

/* Valid color and border values */
.button {
  background-color: #007bff;
  border: 1px solid #0056b3;
}

How to Use CSS Validator?

Using our CSS validator is straightforward and provides comprehensive feedback:

1. Choose Validation Method: Select from "Validate by Input" (paste CSS code), "Validate by URI" (check live website), or "Validate by File Upload" (upload .css files)
2. Configure Settings: Choose your CSS profile (CSS1-3, Mobile, SVG, etc.), media type, and warning level in the settings panel
3. Input Your CSS: Paste your CSS code into the editor, enter a website URL, or upload a CSS file using the file upload button
4. Run Validation: Click the "Validate CSS" button to perform comprehensive W3C standards checking
5. Review Results: Check the validation status and review any errors or warnings displayed with line numbers and detailed explanations
6. Fix Issues: Click on specific error messages to jump to the problematic line in the editor and make corrections
7. Re-validate: Continue validating as you make changes to ensure all issues are resolved
8. Download Clean CSS: Save your validated CSS file once all issues are fixed

Validation Settings & Options

Customize the validation process with these comprehensive options:

Common CSS Validation Issues

The validator detects various types of CSS issues organized by severity:

Best Practices for CSS Validation

• Regular Validation: Validate CSS frequently during development to catch issues early
• Choose Appropriate Profile: Select the CSS profile that matches your target browsers and requirements
• Address Errors First: Fix syntax errors before addressing warnings to ensure proper CSS parsing
• Consider Browser Support: Balance W3C compliance with practical browser compatibility needs
• Use Fallbacks: Provide fallback properties for newer CSS features when targeting older browsers
• Validate External Stylesheets: Check all CSS files including external libraries and frameworks
• Test Across Devices: Validate with different media types to ensure responsive design compatibility
• Document Exceptions: When using vendor prefixes or experimental features, document the reasoning

Note: This validator uses the official W3C CSS validation service. Some modern CSS features or experimental properties may not validate if they're not yet part of the official specification, even if they work in browsers.