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HTML Validator

Find unclosed, mismatched and stray HTML tags, duplicate ids and attributes, and images without alt text.

Runs in your browserHTML → Report
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Example

Input
<div id="a">
  <p>Hello <b>world</p>
</div>
<span id="a"></span>
Output
✗ 2 errors (4 elements checked)

Line 2: Error: <b> (line 2) is not closed before </p> on line 2.
Line 4: Error: Duplicate id "a" (first used on line 1).

How to use the HTML Validator

  1. Paste or type your HTML into the input area, or open a file from your device.
  2. Adjust the options above the editor if the tool offers any.
  3. Review the Report result, then copy it or download it as a file.

Privacy and limitations

  • Your data is processed on your device and is not uploaded to any server.
  • This is a structural checker, not the W3C validator: it does not check which elements and attributes are allowed where.
  • Optional end tags (</p>, </li>, </td>…) are understood and not reported as missing.

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