HTML Validator (Basic)

About this tool

Run a basic check of your HTML for common structural problems like unclosed or mismatched tags. For full conformance use the W3C validator.

Example

Input: <div><p>Hi</div>

Output: Mismatched: expected </p> but found </div>

Privacy

This tool runs entirely in your browser. Your data is processed locally and never uploaded to a server.

How to use this tool

1. Paste your HTML into the input box.
2. Run the check to scan for basic structure problems.
3. Read the reported issues and locate the matching tags in your code.
4. Fix the HTML, then run the validator again to confirm the markup is clean.

Step by step, what happens

1. The tool reads your HTML as plain markup and looks for common structural mistakes such as missing closing tags and tags that do not match their opening pair.
2. It checks nesting so you can spot places where a tag was closed in the wrong order or left open too long.
3. It returns step-by-step explanations that point to the problem area and describe what needs to be fixed.
4. If you need full standards conformance, use this as a quick first pass and then verify the page with the W3C validator.

Worked example

Here is a small example where a paragraph tag is opened but never closed before the next block element starts.

Input: <div><p>Hello</div>

1. The validator scans the opening div and p tags, then notices that the div closes before the p tag is closed.
2. It flags this as mismatched nesting because the tags are not closed in the correct order.
3. It explains that the p tag should be closed before the closing div tag.

Tips and common mistakes

• Use this tool for quick structural checks, but do not treat it as a full standards validator.
• When you see a nesting error, check the order of your closing tags, not just whether the tags exist.
• Make sure each opening tag that needs a closing tag has one, especially in nested sections like div, p, ul, li, and form.
• If the tool points to a problem near one tag, look a few lines above it because the real mistake is often earlier in the markup.

Frequently asked questions