Find a tool

HTML Validator Runs in your browser. No input data is sent to our server.

Paste HTML into the editor, validate it instantly, and review a readable result with warnings or errors. This page is useful for templates, embeds, snippets, and frontend markup checks.

Validation result

Paste content and validate it instantly.

This validator runs in your browser so you can check syntax, spot issues, and copy the result without sending your text to a third-party validation service.

Validate HTML Online

Validate HTML online and get a clear result so markup issues in templates, snippets, embeds, and frontend content are caught before use. Paste your HTML and the validator checks for structural problems — unclosed tags, duplicate attributes, invalid nesting — and returns a readable pass or error result.

How to use HTML Validator

1

Paste content into the html input panel.

2

Run the validator to check for success messages, syntax issues, or invalid structure.

3

Review the result, then copy or download it if you need to share the outcome.

Why this helps in real workflows

A page template or component snippet is not rendering correctly and you want to check whether there are unclosed or improperly nested HTML tags.

An HTML email template or newsletter block needs a markup check before sending to confirm there are no structural issues.

HTML generated by a CMS, page builder, or export tool needs to be validated before it is embedded in another page or sent to a client.

You are debugging a layout issue and want to rule out malformed markup as the cause before investigating CSS or JavaScript.

Common problems and fixes

The validator passes but the page still renders incorrectly.

Browsers are forgiving with HTML and will attempt to render even invalid markup. Passing validation means no structural errors were found, but rendering issues may still be caused by CSS rules, conflicting styles, or missing content — not the HTML structure itself.

The validator reports an error on a tag that looks correct.

Check the reported line number. Common issues include unclosed tags before the error line, an attribute value missing its closing quote, or an element nested in a context that does not allow it — like a block element inside an inline element.

I want to format the HTML as well as validate it.

Use the HTML Formatter to add readable indentation after confirming the markup is valid. The validator checks for errors; the formatter makes it easier to read.

Related tools

Developer Tools Hub OpenAPI & Swagger Validator XML Validator JSON Validator YAML Validator

Related Guides

How to Escape HTML Characters Safely How to Clean Up HTML Into Markdown How to Turn Markdown Into HTML for Publishing

Frequently asked questions

How do I validate HTML?

Paste your HTML into the input box, run the validator, and review the validation result in the output panel.

Will the HTML validator show markup issues?

Yes. The validator reports HTML issues such as unclosed tags, duplicate attributes, and invalid nesting when it detects them.

Is this HTML validator free?

Yes. It is free to use in your browser.

Does this validator check the full HTML5 specification?

The validator checks for common structural issues including unclosed tags, duplicate attributes, and invalid nesting. For full W3C HTML5 conformance checking, the W3C Markup Validation Service at validator.w3.org is the reference tool.

Can I validate just a snippet rather than a full HTML page?

Yes. You can paste any HTML fragment — a component, a section, an email block — and the validator will check its structure. A snippet does not need to include a doctype or full page wrapper.

Can I format the HTML after validating it?

Yes. Once you confirm the HTML is structurally correct, paste it into the HTML Formatter to add consistent indentation.