What is the difference between well-formed and valid?

Well-formed means it obeys XML syntax. Valid means it also conforms to a DTD or schema, which is a separate check this tool does not perform.

XML Validator

Check that a document is well-formed and locate the failure.

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About this tool

Checks whether a document is well-formed — properly nested, correctly quoted, single root — and reports the position of the first failure.

Limitations

Checks well-formedness, not validity against a DTD or XSD. Schema validation needs the schema, and often the network.

Questions

What is the difference between well-formed and valid?: Well-formed means it obeys XML syntax. Valid means it also conforms to a DTD or schema, which is a separate check this tool does not perform.

Privacy

This page does its work in your browser. What you paste is processed by JavaScript running on your own device and is never sent to a DevToolery server — there is no server that could receive it. The page itself is a static file delivered by a CDN. See exactly what is stored.