Web API WCF It is a web Application Programming Interface It is a Windows Communication Foundation It uses HTTP which is suitable for various protocols which support on various browser Multiple protocols like: HTTP, HTTPS, Name Pipes, MSMQ,  etc., are supported and is allowed to switch between any of them Web API   a simple class file with .cs (C#) extension The Extension of WCF service is .svc Web API support JSON or XML It support JSON,XML,ATOM data format It is not open source but it can be understood by the client who knows the Xml If the client knows the XML then it doesn't meant for them