XML Validation

The xmllint tool can be used to validate XML documents against DTDs and XML Schema definitions. It can be downloaded as a part of the free, open-source libxml2 package at http://xmlsoft.org/xmldtd.html.

These are some examples of using the xmllint command.

To validate XML data with a DTD stored in the same file:

xmllint --valid --noout DataFileWithDTD.xml

To validate XML data against a separately stored DTD:

xmllint --dtdvalid DTD.dtd --noout DataFileWithoutDTD.xml

To validate XML data against a separately stored XML Schema definition:

xmllint --schema XMLSchemaFile.xsd --noout DataFile.xml

Alternatively, the following online services can also be used to validate XML:
 * W3C Markup Validation Service for DTDs
 * XML for ASP.NET Schema Validator for XML Schema.