HTML Validate

HTML Validate

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What is HTML Validate

HTML Validate is a free online checker that runs HTMLHint on your markup and reports issues as JSON with severity, location, rule, and message — so you can catch common problems before publishing.

It is not the W3C Nu Html Checker. Use it for everyday HTMLHint-style feedback in the browser, then preview fixed markup in HTML Viewer when you want a visual check.

How to use HTML Validate

  1. Step 1: Add HTML. Paste, Import, Sample, or Fetch URL.
  2. Step 2: Validate. Run Validate and read the JSON issue list.
  3. Step 3: Fix and re-check. Update your source using line/column hints, then Validate again.

HTML Validate Features

  • HTMLHint-based validation in the browser
  • JSON report with severity, line, column, rule, and message
  • Sample, Import, Fetch URL, Copy, Download

Common use cases

  • Pre-publish markup checks: Catch unclosed tags and common rule violations before go-live.
  • Sanitize CMS pastes: Validate HTML copied from a rich-text editor.
  • Email HTML hygiene: Scan templates for structural issues before a campaign send.

Examples / supported formats

Validates HTML and returns a JSON report:

  • HTML input
  • JSON validation report output

After fixes, preview in HTML Viewer or tidy with HTML Formatter.

FAQ

Is HTML Validate free?
Yes. Tools Viewer tools are free to use in the browser with no account required.
Do I need to create an account to use HTML Validate?
No. Open the tool and start working — signup is not required.
Is my content uploaded to your servers?
Pasted or imported content for HTML Validate is processed in your browser. Tools Viewer does not store it. Optional Fetch URL (when available) retrieves a public page through a short-lived request so you can edit the result locally.
Is this the W3C Nu Html Checker?
No. It uses HTMLHint rules in your browser. Use a dedicated conformance checker when you need full W3C validation. After fixing issues, preview in HTML Viewer.
How do I validate HTML online?
Paste your HTML into HTML Validate, click Validate, and review the JSON issue report. Fix reported lines, then run Validate again.