XML Schema to validate XML Schemas?

Of course. Most of the time you can just point your browser to the URL that serves as the namespace for the XML document. This also works with XML Schema: http://www.w3.org/2001/XMLSchema

The XSD is linked from there.

Also check XSOM. This is what JAXB RI uses to load and process XSDs.

There are two versions of the XML Schema Definition Language (XSD): 1.0 and 1.1. Version 1.0 was released in 2001 and version 1.1 was released in 2009.

The normative XSD schemas are:

• http://www.w3.org/2001/XMLSchema.xsd
• http://www.w3.org/2009/XMLSchema/XMLSchema.xsd

You can test the validation of an XSD schema via the command line, e.g.:

$ xmllint -noout -schema XMLSchema.xsd myschema.xsd