Check your XML
Mismatched tags, undefined entities, broken namespaces — found and located precisely, by the browser's own XML parser. Nothing is uploaded.
- Processed on your device
- No upload, no waiting
- No signup, no watermark
Paste XML and it is checked as you type.
How it works
Paste your XML
Or drop the file in. Nothing is sent anywhere.
Read the verdict
Well-formed, with a summary of what is inside. Or the exact line and column of the first problem.
Fix and re-check
Edit in place; the answer updates as you type.
Frequently asked questions
Is my XML uploaded?
No. There is no upload, no server call and no logging — the formatting happens inside this page, on your own device. You can disconnect from the internet after the page loads and it keeps working. That matters here more than it looks: the things people paste into an online JSON formatter are API responses, config files and error payloads, and those routinely carry tokens, customer records and internal hostnames.
What does "well-formed" mean?
That the document obeys XML's own rules: every tag closed, tags nested in the right order, exactly one root element, attributes quoted, and every & and < either escaped or part of a valid entity. It is the first of two questions you can ask about XML. The second — whether the document matches a particular schema — is separate, and this page does not answer it.
Does it validate against a DTD or XSD schema?
No. This checks that the document is well-formed XML, which is the failure most people are actually looking at. Schema validation needs your schema file and a validating parser, and no browser ships one; claiming to do it here would mean either sending your document to a server or quietly not checking. The distinction is worth knowing: a document can be perfectly well-formed and still wrong for its schema.
What are the most common XML errors?
A bare ampersand is the usual one — & must be written &, even inside a URL, so a query string pasted straight into an element breaks the document. After that: a tag closed in the wrong order, two root elements, an undefined entity like (which HTML defines and XML does not), and a namespace prefix used without being declared. Each is reported by name with its position.
Is HTML valid XML?
Usually not, and that is normal rather than a mistake. HTML allows unclosed tags like <br> and <li>, unquoted attributes and bare ampersands; XML allows none of them. If you need HTML that is also valid XML, that is XHTML, and it must close every tag.
Is there a size limit?
Your device's memory rather than an upload cap. Documents of a few megabytes format instantly; very large ones are limited by how much the browser will hold, not by anything we impose.