This is an open-source C# project (web forms) that compares any gbXML file (created by Revit, for example) against the version 6.01 XSD schema.
This validator only checks for valid gbXML and does not do any type of test case validation. The source code also includes a C# class that represents the entire gbXML schema version 6.01 (created using XSD.exe).
Created by Stephen Roth for Carmel Software Corporation on behalf of gbXML.org.