HTML Validator

Validate HTML syntax and structure. Check for errors and warnings in your HTML code.

HTML Input

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  Test


  
    Unclosed paragraph

<!DOCTYPE html>
<html>
<head>
  <title>Test</title>
</head>
<body>
  <div>
    <p>Unclosed paragraph
  </div>
</body>
</html>

Catch HTML Errors Before They Break Your Pages

Invalid HTML can cause broken layouts, inaccessible pages, and SEO penalties. This validator scans your markup in real time, flags unclosed tags, mismatched nesting, and other structural problems so you can fix them before they reach users.

Instant Syntax Checking

Why Use This Tool?

Find Structural Errors Fast

Instantly locate unclosed tags, mismatched elements, and nesting violations that cause cross-browser rendering differences.

Prevent Layout Bugs

Broken HTML structure is a leading cause of layout bugs in CSS. Validate first to eliminate a whole class of hard-to-diagnose issues.

Improve Accessibility & SEO

Valid, well-structured HTML is easier for screen readers and search engine crawlers to parse, supporting both accessibility and rankings.

100% Private

All validation runs locally in your browser. Your HTML is never sent to or stored on any server.

How this HTML Validator works

This syntax checking tool scans HTML code for common structure errors and validity issues. It identifies unclosed tags, mismatched nesting, missing attributes, and other syntax violations that might break page rendering. While not a full W3C validator substitute, it provides immediate feedback on basic structure, expanding self-closing tags, and highlighting logic errors. It helps developers catch layout-breaking bugs quickly before deploying code.

How to use this HTML Validator

Paste Your HTML

Paste any HTML snippet or full document into the input field.

Validate

The validator scans for unclosed tags, mismatched nesting, missing attributes, and other syntax issues.

Review Errors

Read the highlighted error messages and fix each issue before deploying your code.

Example Usage

Detect an unclosed paragraph and bold tag inside a div element.

Input

<div><p>Hello <b>World</div>

Output

Error: Unclosed tag <p> — missing </p> before </div>. Error: Tag <b> is not closed.

Frequently Asked Questions

What does an HTML validator check?

It checks for unclosed tags, mismatched nesting, invalid attribute usage, missing required attributes, and other structural issues that can break page rendering across different browsers.

Is this the same as the W3C HTML validator?

No. This is a fast, browser-based checker that catches common structural errors. The W3C validator applies the full HTML specification and is more thorough for standards compliance.

My page looks fine in the browser — why does the validator report errors?

Browsers are forgiving and silently correct many HTML errors. Validation catches issues that may cause inconsistent rendering in other browsers, screen readers, or search engine crawlers.

Can I validate a full HTML document including DOCTYPE and head tags?

Yes. Paste the complete document including the DOCTYPE declaration, head, and body. The validator handles partial snippets and full documents.

Is this HTML validator secure?

Yes. Validation runs entirely in your browser. Your HTML code is never transmitted to or stored on any server.

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The HTML Validator is maintained by CodeItBro. We aim to provide the best free developer tools on the web. If you have feedback or suggestions, please visit our contact page.

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