HTML Accessibility Checker
Our HTML accessibility checker helps you test HTML code for WCAG 2.1 AA compliance. Check accessibility to ensure your website is usable by everyone, including users with disabilities. Test for missing alt text, improper heading hierarchy, missing ARIA labels, form label issues, and keyboard navigation problems. All checking happens locally in your browser.
- WCAG Level
- 2.1 AA
- Standards
- WCAG 2.1
- Mode
- In-browser
- Price
- Free
WCAG 2.1 AA
Tests against WCAG 2.1 Level A and AA standards for complete accessibility compliance.
ARIA & Labels
Validates ARIA attributes, form labels, and semantic HTML structure.
100% Private
Everything runs locally. Your HTML never leaves your device.
Check HTML accessibility online
Paste your HTML code, click Check Accessibility, and review the WCAG 2.1 compliance results with errors, warnings, and suggestions.
Demo fetch uses a CORS-friendly approach only if the target allows it.
Privacy-first
This page processes content locally in your browser (no upload).
What is HTML Accessibility Checking?
HTML accessibility checking is the process of testing HTML code against WCAG 2.1 (Web Content Accessibility Guidelines) standards to ensure your website is usable by everyone, including people with disabilities. An HTML accessibility checker analyzes your code to detect accessibility barriers that prevent users with visual, auditory, motor, or cognitive disabilities from accessing your content.
When you build websites, it's essential to ensure they're accessible to all users. Missing alt text on images prevents screen reader users from understanding images. Missing form labels make forms unusable for assistive technology users. Improper heading hierarchy confuses screen reader navigation. An HTML accessibility checker helps you identify and fix these issues to achieve WCAG 2.1 AA compliance, which is often required by law and essential for inclusive web design.
✗Invalid HTML
<!DOCTYPE html>
<html>
<head>
<title>Example</title>
</head>
<body>
<h1>Welcome</h1>
<p>This paragraph is not closed
<img src="image.jpg">
<a href="link.html">Click here
</body>
</html>Missing closing tags, missing alt text, unclosed elements
✓Valid HTML
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Example</title>
</head>
<body>
<h1>Welcome</h1>
<p>This paragraph is closed.</p>
<img src="image.jpg" alt="Description">
<a href="link.html">Click here</a>
</body>
</html>All tags closed, proper structure, accessibility attributes
What Does HTML Validation Check?
- •Syntax Errors: Missing closing tags, mismatched tags, invalid characters, and malformed HTML structure
- •Required Elements: DOCTYPE declaration, html tag, head tag, title tag, body tag, and other essential HTML5 elements
- •Accessibility Issues: Missing alt text on images, missing lang attribute, improper heading hierarchy, missing ARIA labels, and other WCAG compliance issues
- •SEO Problems: Missing meta description, missing Open Graph tags, improper heading structure, missing title tag, and other SEO best practices
- •Performance Warnings: Missing lazy loading on images, oversized images, missing optimization attributes, and other performance issues
- •Security Issues: External links missing rel="noopener", insecure resources, and other security best practices
According to W3C WCAG 2.1 guidelines, accessible HTML is the foundation of inclusive web content. Missing alt text, improper heading hierarchy, and missing ARIA labels break screen readers, cause navigation issues, and create barriers for users with disabilities. Our HTML accessibility checker tests for WCAG 2.1 Level A and AA compliance to ensure your website is accessible to everyone.
Modern web development workflows should include HTML accessibility checking as a standard step. Whether you're building a new website, maintaining existing code, or learning HTML, using an HTML accessibility checker helps ensure your code is accessible, legally compliant, and usable by all users. For more information on accessibility standards, see the W3C WCAG 2.1 guidelines, MDN Accessibility documentation, and Google's accessibility guide.
HTML Validation Impact
Real data showing the importance of validating HTML code
Validation Statistics
According to W3C accessibility research, over 98% of websites have accessibility barriers that prevent users with disabilities from accessing content. Missing alt text, improper heading hierarchy, missing form labels, and keyboard navigation issues are common problems. Regular HTML accessibility checking helps catch and fix these issues to achieve WCAG 2.1 compliance and ensure your website is accessible to everyone.
Why Check HTML Accessibility?
Checking HTML accessibility is essential for building inclusive, legally compliant, and user-friendly websites. Here's why you should make accessibility checking part of your development workflow:
Ensure Browser Compatibility
Invalid HTML can render differently across browsers. Chrome, Firefox, Safari, and Edge may handle errors inconsistently, leading to layout breaks, missing content, or broken functionality. Valid HTML ensures consistent rendering across all browsers and devices, reducing cross-browser testing time and user complaints.
Improve Accessibility
Inaccessible HTML breaks screen readers and assistive technologies. Missing alt text prevents screen reader users from understanding images. Improper heading hierarchy confuses navigation for users with screen readers. Missing ARIA labels and form labels make interactive elements unusable. Accessible HTML with proper semantic structure, ARIA attributes, and keyboard navigation is the foundation of WCAG 2.1 compliance. This is not just best practice—it's often a legal requirement under ADA, Section 508, and similar laws worldwide.
Boost SEO Rankings
Search engines like Google prefer valid, well-structured HTML. Missing meta tags, improper heading hierarchy, and invalid structure can hurt your search rankings. Valid HTML with proper semantic structure helps search engines understand and index your content better, potentially improving your rankings and organic traffic.
Catch Errors Early
HTML validation catches errors before they cause problems in production. Missing closing tags, invalid attributes, and structural errors can lead to broken layouts, JavaScript failures, and user experience issues. Validating during development saves debugging time and prevents costly fixes after deployment.
Improve Performance
Invalid HTML can cause browsers to spend extra time parsing and fixing errors, slowing down page rendering. Valid HTML renders faster, improving Core Web Vitals metrics like First Contentful Paint (FCP) and Largest Contentful Paint (LCP). Faster pages provide better user experience and can improve search rankings.
Enhance Security
Valid HTML helps prevent security vulnerabilities. Missing rel="noopener" on external links can expose your site to tabnabbing attacks. Invalid HTML can also make your site more vulnerable to XSS attacks. Validating HTML helps ensure you're following security best practices and protecting your users.
How It Works
Our HTML validator uses client-side parsing and rule checking to validate your HTML code. Here's how the validation process works:
Parse HTML Structure
The validator parses your HTML code to identify all tags, attributes, and structure. It builds a tree representation of your document and checks for proper nesting and hierarchy.
Check Syntax Errors
The validator checks for missing closing tags, mismatched tags, invalid attributes, missing required elements (DOCTYPE, html, head, body, title), and other syntax errors that break HTML validity.
Validate Accessibility
The validator checks for accessibility issues including missing alt text on images, missing lang attribute, improper heading hierarchy (h1 should be first, no skipped levels), missing ARIA labels, and other WCAG compliance issues.
Check SEO & Performance
The validator checks for SEO issues (missing meta description, missing Open Graph tags, improper heading structure) and performance warnings (missing lazy loading, security issues with external links). It generates a comprehensive report with errors, warnings, and suggestions.
Best Practices for HTML Validation
Follow these best practices to ensure your HTML code is valid, accessible, and optimized:
Always Include DOCTYPE
Every HTML document should start with <!DOCTYPE html>. This tells browsers which HTML version to use and ensures proper rendering. Without it, browsers may enter quirks mode, causing inconsistent rendering.
✅ DO: <!DOCTYPE html>
❌ DON'T: Skip DOCTYPE declaration
Close All Tags Properly
Every opening tag must have a corresponding closing tag (except self-closing tags like <img>, <br>). Mismatched or unclosed tags can break layout and functionality.
Test regularly: Validate HTML after major changes, before deployment, and as part of your build process
Use Semantic HTML
Use semantic HTML5 elements like <header>, <nav>, <main>, <section>, <article>, and <footer>. These improve accessibility, SEO, and code maintainability.
Semantic benefits: Better accessibility • Improved SEO • Easier maintenance • Clearer code structure
Add Accessibility Attributes
Always include alt attributes on images, lang attribute on html tag, proper heading hierarchy (h1 → h2 → h3), and ARIA labels where needed. These are required for WCAG 2.1 compliance.
Accessibility checklist: Alt text on images • Lang attribute • Proper headings • ARIA labels • Keyboard navigation
Include Essential Meta Tags
Add essential meta tags for SEO and functionality: charset, viewport, description, and Open Graph tags for social sharing. These improve SEO rankings and user experience.
Essential meta tags: charset="UTF-8" • viewport for mobile • description for SEO • og:tags for social
Validate Regularly
Validate your HTML code regularly—after major changes, before deployment, and as part of your build process. Use automated validation in CI/CD pipelines to catch errors early. Regular validation prevents issues from accumulating and becoming harder to fix.
Validation schedule: After code changes • Before deployment • In CI/CD pipeline • During code reviews
Frequently Asked Questions
How do I validate HTML code?
Paste your HTML code into the validator, click Validate, and review the results. The tool checks for syntax errors, missing tags, accessibility issues, SEO problems, and performance warnings. All validation happens locally in your browser for complete privacy.
What HTML errors does the validator detect?
Our HTML validator detects missing DOCTYPE, unclosed tags, mismatched closing tags, missing required elements (html, head, body, title), invalid attributes, and structural issues. It also checks for accessibility problems like missing alt text and SEO issues like missing meta tags.
Do you store my HTML code?
No. This HTML validator processes everything locally in your browser. Your code never leaves your device, ensuring complete privacy and security. No server uploads, no data storage, no privacy concerns.
What's the difference between errors and warnings?
Errors are critical issues that break HTML validity or functionality (missing closing tags, invalid structure). Warnings are important but non-critical issues (missing alt text, missing meta tags). Suggestions are best practices for better SEO, accessibility, and performance.
Does this validator check for accessibility issues?
Yes. Our HTML validator checks for accessibility issues including missing alt text on images, missing lang attribute, improper heading hierarchy, missing ARIA labels, and other WCAG compliance issues. This helps ensure your HTML is accessible to all users.
Can I validate HTML from a URL?
Yes. You can fetch HTML from a URL using the fetch feature, though it may be blocked by CORS policies. Alternatively, copy the HTML source code from your browser's developer tools and paste it into the validator for complete validation.
What SEO issues does the validator check?
The validator checks for missing meta description, missing Open Graph tags, improper heading hierarchy (h1 should be first, no skipped levels), missing title tag, and other SEO best practices. These checks help improve your search engine rankings.
Is this validator based on W3C standards?
Yes. Our HTML validator follows W3C HTML5 standards and checks for compliance with official HTML specifications. It validates syntax, structure, and best practices according to W3C guidelines and modern web standards.
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