Want a Custom tool for Yourself?

Need a Custom Tool? We build custom tools that can save hours per employee per day.

HTML Validator

Check HTML for common syntax issues and invalid structure. Paste your content and get a quick pass or fail result with details. Runs in your browser.

HTML Validator


OR


 

Result will appear here...

SIMILAR TOOLS


Last updated: February 21, 2026

Created by: Eon Tools Dev Team

Reviewed by: Sugam Baskota


What this does

So you want to know whether your HTML is actually valid, not just whether it looks right in the browser, which is forgiving and will paper over plenty of mistakes. This checks it properly. Paste your HTML or upload a file, choose whether it is a full page or a fragment, press Validate, and you get the verdict with any problems listed.

How to use it

  1. Paste your HTML, or upload an .html file.
  2. Choose Fragments: No for a complete page, Yes for a snippet that is only part of a page.
  3. Press Validate and read the result.

How it works

How it checks depends on which option you pick. For a full page, with Fragments set to No, it sends your HTML to the official W3C Nu Html Checker, the same validator the standards body itself runs, and reports back exactly what it finds, including the line and column of each issue. That does mean your HTML is sent to the W3C service to be checked, which is worth knowing if the page contains anything sensitive.

For a fragment, with Fragments set to Yes, it runs a quick check in your browser instead, parsing the snippet and looking for obvious problems like tags that do not match up. Nothing leaves your machine in that mode.

What each mode catches

The two modes are doing different jobs. The full check is the thorough one, since it runs your page against the real HTML specification and will flag everything from a mistyped attribute to a misnested element. It is the option to reach for when you want a proper answer.

The fragment check is lighter, meant for snippets that are not whole pages, where the full validator would complain about the missing document structure. It is a rough and ready look rather than a complete audit, so treat a clean fragment result as a good sign rather than a cast iron guarantee.

Questions people ask

What is the difference between a page and a fragment?

A page is a complete HTML document, with its doctype and <html> structure. A fragment is a snippet, like a single section, meant to sit inside a page. Choose the one that matches what you pasted.

Is my HTML sent anywhere?

For a full page check, yes, it is sent to the official W3C validator to be checked. For a fragment check, no, that runs entirely in your browser.

Why does the browser show my page fine but the validator complains?

Browsers are deliberately forgiving and will quietly fix or ignore many mistakes. The validator holds your HTML to the actual specification, so it reports things the browser lets slide.

Does valid HTML mean my page is correct?

It means the markup follows the rules. It does not judge whether the page looks right or does what you intended, which is a separate matter.

References

  1. World Wide Web Consortium. Nu Html Checker. https://validator.w3.org/nu/
  2. MDN Web Docs. HTML: HyperText Markup Language. https://developer.mozilla.org/en-US/docs/Web/HTML

Sugam Baskota

Sugam Baskota is a senior software engineer and Computer Science graduate from UT Arlington, with interests in user scripts, browser extensions, developer tooling, and productivity systems. He spends time building practical utilities and extensions in the kinds of workflows Eon is designed to simplify. At Eon Tools, he reviews useful, password, and developer tools.

Other Tools