HTML Validator
Check HTML for errors, warnings, and web standards compliance
HTML Input
📊 Validation Results
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Errors
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Warnings
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Info
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Score
Ready to validate
Paste your HTML code and click "Validate HTML" to check for errors and issues.
❌ Common Errors
• Unclosed tags: <p>Text without closing
• Missing alt attributes on images
• Invalid nesting: <p><div>Invalid</div></p>
• Missing DOCTYPE declaration
• Duplicate IDs in the same document
⚠️ Common Warnings
• Missing meta viewport tag
• Empty href attributes
• Missing title element
• Obsolete HTML attributes
• Inline styles without proper structure
♿ Accessibility Issues
• Images without alt text
• Form inputs without labels
• Missing heading hierarchy
• Poor colour contrast
• Missing ARIA attributes
🔍 SEO Problems
• Missing meta description
• Multiple H1 tags
• Empty title tags
• Missing Open Graph tags
• Poor heading structure
🎯 What is HTML Validation?
HTML validation is the process of checking HTML markup against web standards to ensure it's syntactically correct and follows best practices for accessibility, SEO, and performance.
Why validate HTML? Valid HTML ensures consistent rendering across browsers, better accessibility for users with disabilities, improved SEO rankings, and easier maintenance of your code.
Web standards: Our validator checks against HTML5 standards and modern web development best practices.
🔧 Validation Categories
- Structure validation: Checks proper nesting, closed tags, and document structure
- Attribute validation: Validates HTML attributes, values, and required attributes
- Accessibility checks: Identifies barriers for users with disabilities
- SEO validation: Checks for search engine optimisation best practices
- Performance hints: Suggests improvements for faster loading
- Strict mode: Applies additional rules for high-quality code
- Cross-browser compatibility: Identifies potential browser-specific issues