All toolsW3C Validation
Validate a page's HTML
CrawlOut runs the page's markup through the real W3C Nu HTML Checker for spec-level errors, and its own pass for bad coding structure — obsolete tags, broken heading order, duplicate ids, missing landmarks — that validates fine but is still worth fixing.
<!DOCTYPE html>
<html lang="en">
<head>…</head>
<body>
<h1>…</h2> // mismatched tag
</body>
</html>
Spec-Level ChecksW3C Nu HTML Checker
Structure Passlandmarks & heading order
Real W3C CheckerRuns the official Nu HTML Checker, not a lookalike.
Structure PassCatches obsolete tags, heading order, missing landmarks.
Line-Level DetailEvery issue points to the exact line and snippet.
One Click, Full ReportNo install, no upload — just the URL.
Learn more
Understanding HTML validation
A few common questions about what validation checks for and why it matters.