A technique for synthesizing tests from a Web service document includes locating at least one parameter for at least one client to server function call in a Web service document. Client validation constraints for the at least one parameter are discovered. Server validation constraints for the at least one parameter in the Web service document are discovered. At least one range for the at least one parameter that will be accepted by the server and not be accepted by the client is discovered. Tests using parameter values from the discovered at least one range are synthesized.