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Guide

How to use this tool, examples, and related tips.

How to Use the HTML Validator

Paste your HTML document or fragment into the input field.

The tool parses the markup using the browser's DOMParser and reports any structural errors or issues it detects.

Review the flagged issues and correct them in your source.

Note: This tool validates HTML using the browser's built-in DOMParser — it is not a full W3C validator. The browser parser is lenient by design and will auto-correct many errors silently. For strict W3C compliance checking, use the official W3C Markup Validation Service at validator.w3.org.

What Is HTML Validation?

HTML validation checks a document against the HTML specification to identify markup errors — unclosed tags, invalid nesting, deprecated elements, missing required attributes, and structural issues. A valid HTML document renders more predictably across browsers, is more accessible to screen readers, and is less prone to rendering bugs caused by browser error-correction behavior. There are two levels of validation: parser-level checks (what this tool performs) and full specification compliance checks (what the W3C validator performs).

When to Use This Tool

Catching obvious markup errors — Quickly check for unclosed tags, mismatched elements, or malformed attributes in hand-written HTML.

Validating HTML fragments — Check snippets like email templates, CMS components, or embedded widgets without setting up a full validation pipeline.

Pre-flight checks before deployment — Run a quick structural check on HTML files before pushing to production.

Learning HTML — Use validation feedback to understand which markup patterns are structurally incorrect.

Related Tools

  • HTML formatter
  • HTML minifier
  • HTML escape
  • CSS validator
  • XML validator

FAQ

Answers about this tool and how your data is handled.

Is this a full W3C validator?

No. This tool uses the browser's DOMParser, which is lenient — it auto-corrects many errors without reporting them. For strict W3C HTML5 compliance validation, use validator.w3.org.

What kinds of errors does this tool catch?

Structural issues that the DOMParser surfaces — severely malformed markup, invalid nesting in some cases, and parse failures. It will not catch all specification violations.

Does this tool validate against the HTML5 spec?

It uses the browser's HTML5 parser, so it reflects how a modern browser interprets the markup. It does not perform spec-level conformance checking.

Does this tool send my data to a server?

No. Validation runs entirely in your browser. Nothing is uploaded.

Can I validate HTML email templates with this tool?

You can check for basic structural issues. HTML email validation is a separate discipline — email clients have their own rendering quirks that this tool does not account for.

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