What is WSDL?

As XML Web Services (think HTTP and SOAP) are becoming more common, applications need a standard way to describe the operations offered by a service. Web Services Description Language (WSDL) is an XML based language that describes how clients communicate with a web service.

A WSDL document specifies the available operations, input and output messages, supported protocols, and the service endpoint URL. The WSDL document (file or URL) sits between then client and the service:

Client <> WSDL <> SOAP Service

Development tools can read a WSDL document and automatically generate client code (like proxy classes), making it much easier to call remote services. ASP.NET Web Services automatically expose a WSDL document by appending ?WSDL to the service URL:

http://server/MyService.asmx?WSDL

The generated description can then be used by development tools to build strongly typed client code without manually constructing SOAP messages. For more information, see the W3C Web Services Description Language (WSDL) specification and the Microsoft ASP.NET documentation.