HTML & Markup
HTML Validator Helper
Paste HTML to catch common structural mistakes — unclosed and mismatched tags, duplicate ids, missing alt text, obsolete elements — each with a plain-language fix. Everything runs in your browser — your markup never leaves the page.
HTML source
paste a page or fragmentChecked with a string-based parser: script and style contents are skipped, and pasted code is never executed.
Results
liveHow it works
Your HTML is scanned with a lightweight string-based parser that tracks the open-element
stack. It reports the mistakes that most often break layouts and accessibility:
<div> tags that are never closed, closing tags with no opening,
mismatched nesting, duplicate id values, images without alt,
obsolete elements, and missing document basics such as <!DOCTYPE html>
and lang. Every finding includes the line number and a concrete fix.
Nothing is sent to a server.