HTML Validator

Validate HTML markup for syntax errors, unclosed tags, missing attributes, and structural issues. All checks run in your browser.

Drop an .html file here or browse

HTML:

Try examples:

Valid page Fragment Unclosed tags Bad nesting Deprecated tags

How It Works

This tool parses your HTML using the browser's native DOMParser and performs additional structural checks against common HTML rules. All processing happens entirely in your browser — no data is sent to any server.

What Gets Checked

Well-formed HTML structure (properly opened and closed tags)
Void elements used correctly (e.g., <img>, <br>, <input>)
Required attributes (e.g., alt on images, href on links)
Deprecated elements (e.g., <font>, <center>, <marquee>)
Proper nesting (e.g., no <p> inside <p>)
Document structure (<!DOCTYPE>, <html>, <head>, <body>)
Duplicate id attributes

Common HTML Errors

Error	Example	Fix
Unclosed tag	`<div><p>text</div>`	`<div><p>text</p></div>`
Missing alt	`<img src="a.png">`	`<img src="a.png" alt="desc">`
Duplicate id	`<div id="x"><div id="x">`	Use unique `id` values
Deprecated tag	`<center>text</center>`	Use CSS `text-align: center`
Bad nesting	`<a><a>link</a></a>`	Don't nest `<a>` tags

Tip: This validator checks for common issues but does not perform full W3C specification validation. For official validation, use the W3C Markup Validation Service.

Embed This Util

You can embed this util on your own site as a widget. Adding ?embed=1 to the URL loads a compact version with just the tool itself; no header, menu, or documentation. Paste this snippet into your HTML:

Copy snippet Adjust the height to taste.

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