High Quality Content by WIKIPEDIA articles! The Web Services Description Language (WSDL, pronounced `wiz-dul`) is an XML-based language that is used for describing the functionality offered by a Web service. A WSDL description of a web service (also referred to as a WSDL file) provides a machine-readable description of how the service can be called, what parameters it expects and what data structures it returns. It thus serves a roughly similar purpose as a Method signature in a programming language.