Is my HTML uploaded anywhere?

No. Validation runs entirely in your browser with a lightweight parser. Your markup never leaves the page and nothing is stored.

Is this a full W3C validator?

No. It checks tag nesting and closing only — unclosed tags, mismatched close tags, and unexpected closing tags. It does not check attributes, deprecated elements, ARIA, or document conformance; use the W3C validator for a full audit.

Why are and not flagged as unclosed?

Void elements (area, base, br, col, embed, hr, img, input, link, meta, param, source, track, wbr) never take a closing tag, so the checker treats them as self-closing. Explicit self-closing syntax like is also accepted, and HTML comments are skipped.

Validador HTML

Overview

Broken tag nesting is the classic cause of layouts that collapse in one browser but not another. This tool scans your markup with a stack-based checker and reports every structural problem with its line number: tags that are never closed, closing tags with no matching opener, and elements closed in the wrong order. Void elements and comments are handled correctly, so <img> or  never produce false positives.

How to use

Paste your markup into the HTML field — validation runs on every keystroke.
Read the issue list below the field; each entry shows Line N: and the problem.
Fix the flagged lines until you see No nesting issues found.

Examples

<div><p>unclosed</div> → Line 1: <p> is not closed before </div>
<section></article> → Line 1: Unexpected closing </article>
<ul><li>one → Line 1: <ul> is never closed and Line 1: <li> is never closed

Notes

This checks tag nesting and closing only — it is not a full W3C conformance check. Attribute syntax, entity encoding, and semantic rules are out of scope. Issues are sorted by line number, so work top-down: one missing close tag often cascades into several reports.