There are a number of web services that use markup languages:
JSON-WSP
Web template
Web Services Description Language (WSDL), developed by the W3C
XML Interface for Network Services (XINS), provides a POX-style web service specification format
Web Services Conversation Language (WSCL)
Web Services Flow Language (WSFL), superseded by BPEL
WS-MetadataExchange
Representational state transfer (REST) versus remote procedure call (RPC)