HTML Validator
Validate HTML syntax, structure, and common markup issues with html-validate.
HTML Validator
Validate HTML snippets and pages with html-validate before you paste markup into templates, docs, CMS fields, or component examples.
What it checks
- Missing required elements and attributes
- Invalid nesting, closing tags, and document structure
- Accessibility-focused markup issues from the recommended rule set
How to use HTML Validator
The HTML validator checks markup with html-validate so you can catch broken nesting, missing attributes, and document structure issues before using a snippet.
Developers often use this page when they need html validator, html checker, html linter, and html syntax checker.
Privacy and data handling
This tool is designed to run in your browser for normal use, so your input does not need to be sent to a server.
- Input and output stay on the page while you work.
- Copy buttons use your browser clipboard permission when available.
- Avoid pasting private production data on shared or untrusted devices.
Examples
Catch a missing image alt
Input
<main><h1>Docs</h1><img src="diagram.png"></main>Output
Error: <img> is missing required alt attributeThe recommended rule set catches common structure and accessibility issues.
Steps
- 1Paste HTML into the input.
- 2Review errors and warnings with line and column numbers.
- 3Fix the markup and copy the cleaned snippet.
Common use cases
- Check template snippets before sharing.
- Find invalid HTML copied from a CMS field.
- Review accessibility-related markup warnings.
Practical tips
- Validation is stricter than a browser preview.
- Use HTML Previewer when you also need to see the rendered result.
- Validate generated markup before adding it to docs or examples.
FAQ
Does this use a real HTML validator?
Yes. It uses the open-source html-validate package and its recommended rule set.
Why does the browser still render invalid HTML?
Browsers recover from many markup mistakes, but validators help find issues before they become layout, accessibility, or maintenance problems.