What is HTML Validator?
HTML Validator is a free online tool that checks your HTML code for syntax errors, best practices, and accessibility issues. Whether you're building a simple webpage or a complex web application, this tool helps ensure your HTML is properly structured and follows web standards.
Our validator checks for common mistakes like unclosed tags, incorrect nesting, missing attributes, and accessibility concerns, providing detailed feedback to help you write better code.
Why Use HTML Validator?
- Error Detection — Find syntax errors before they cause problems
- Accessibility Checks — Ensure your HTML is accessible to all users
- Best Practices — Get recommendations for proper HTML structure
- Real-Time Validation — See results as you type
- Browser Compatibility — Write code that works across browsers
- SEO Benefits — Proper HTML helps search engines understand your content
Common HTML Errors
| Error | Description |
|---|---|
| Unclosed Tags | Tags that aren't properly closed |
| Incorrect Nesting | Block elements inside inline elements |
| Missing alt on images | Accessibility issue for screen readers |
| Missing DOCTYPE | Page may render in quirks mode |
| Unquoted Attributes | Attribute values should always be quoted |
| Deprecated Tags | Using old HTML tags instead of modern alternatives |
HTML5 Semantic Elements
Use semantic HTML5 elements for better structure and accessibility:
- <header> — Page or section header
- <nav> — Navigation links
- <main> — Main content area
- <article> — Self-contained content
- <section> — Thematic grouping
- <aside> — Sidebar content
- <footer> — Page or section footer
Accessibility Best Practices
- Always include alt text for images
- Use proper heading hierarchy (h1 → h2 → h3)
- Add lang attribute to html element
- Use semantic elements for structure
- Provide labels for form inputs
- Ensure sufficient color contrast
Frequently Asked Questions
What is the difference between HTML validation and linting?
Validation checks if your HTML conforms to the official HTML specification. Linting goes further by checking for best practices, coding style issues, and potential bugs beyond syntax errors.
Why is valid HTML important?
Valid HTML ensures consistent rendering across browsers, better accessibility, improved SEO, and easier maintenance. Browsers are forgiving, but invalid HTML can cause unexpected issues.
Does this tool check CSS or JavaScript?
No, this tool focuses on HTML validation. For CSS validation, use our CSS Validator tool. JavaScript linting requires a different type of tool.
Can I validate HTML from a URL?
Yes! Click "Validate from URL" and enter the web page URL. The tool will fetch and validate the HTML.