Online tool for validating xml against xsd
The function ensures that your document is compliant with the rules defined by an associated DTD, XML Schema, Relax NG, or Schematron schema.XML Schema or Relax NG schema also allows you to embed Schematron rules.
Operating system: Anything Unix, OS X I wrote one in Java for my own use - Java has XML parsing libraries that validate against XSD.
However, see xmllint may be suitable, It may well be already present in a Linux system.
You can validate XML documents by URL, by file upload or by direct input.
Furthermore, you can validate fragments of XML documents.
The XML Schema Working Group, part of the XML Activity, is responsible for the W3C's work on this topic -- for details see the Working Group's charter.