HTML Validator

Validate HTML structure and detect unclosed tags, missing attributes, and syntax issues.

100% Client-Side Local Execution

Upload Data

1

<div class="card"><h2>Title</h2><p>This is valid HTML.</p></div>

<div class="card"><h2>Title</h2><p>This is valid HTML.</p></div>

Valid HTML Structure

No unclosed tags, duplicate closing tags, or missing required properties found.

1

<div class="card"><h2>Title</h2><p>This is valid HTML.</p></div>

<div class="card"><h2>Title</h2><p>This is valid HTML.</p></div>

What is HTML Validator?

The HTML validator checks your markup against HTML specification rules, flagging issues like unclosed tags, invalid nesting, deprecated attributes, and missing required elements — the same category of checks popularized by the W3C's validator. It's aimed at developers who want a w3c html check style validation pass without leaving the browser tab.

Technical Execution

The tool parses your HTML and checks it against known HTML spec rules: proper element nesting (for example, a <p> can't contain a <div>), required attributes, deprecated or obsolete tags, and unclosed elements, then reports each violation with its location in the source.

Zero Data Storage Guarantee

Validation happens entirely client-side, so the markup you're checking — which may be an unpublished page, internal tool, or client project — is never uploaded to a third-party server.

How to Use HTML Validator (Step-by-Step Guide)

Paste the HTML document or snippet you want to validate
Review the list of validation errors and warnings
Check each flagged line for nesting, attribute, or syntax issues
Fix the issues in your source markup
Re-validate until the document passes clean

Frequently Asked Questions (FAQ)

Q: Is this the same as the official W3C HTML validator?

A: It performs the same category of checks — spec-compliant nesting, deprecated tags, missing attributes — as the well-known W3C validator, giving you that w3c html check style feedback without leaving this page.

Q: What's the difference between HTML validator and HTML lint?

A: They describe the same general activity — checking HTML against correctness rules — with 'lint' being the more code-review-flavored term some developers use interchangeably.

Q: Does it catch invalid nesting, like a div inside a p tag?

A: Yes, invalid parent-child element combinations defined by the HTML content model are flagged as errors.

Q: Can I validate HTML online for free without limits?

A: Yes, there's no account requirement or usage cap.

Q: Does it flag deprecated tags like <center> or <font>?

A: Yes, obsolete elements and attributes that are no longer part of the current HTML spec are flagged so you can update to modern equivalents.

Q: Will it validate accessibility issues too?

A: No, this checks HTML spec compliance (syntax and structure), not accessibility (WCAG) rules, which require a separate type of audit.

Q: Does it validate a full page or just a fragment?

A: It can validate a full document including doctype and head/body structure, or a markup fragment, though a fragment may produce warnings about missing document-level elements.

Q: Is there a size limit for validating HTML pages?

A: No fixed limit, though very large pages may take slightly longer given parsing runs in the browser.

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