The is a must to know thing if you wish to work on API's or wonder what is the basic difference between SOAP and REST API's.

Basically, Rest is a architectural design where as Soap is a information exchange protocol.

So, we can't compare both but we can compare the web services built using Rest and Soap

API

First, let's get a brief information about API's

• API is just a tool to interact with web services.
• Its stand for Application programming interface.
• API used to interact with the Restful HTTP web service is called Rest API while the API used to interact with Soap web service is called the Soap API.

Let us understand the difference between Rest and Soap web services to get a clear idea.

Restful HTTP web service

• Rest stands for Representational State Transfer.
• It uses the Rest architectural design and communicates over HTTP protocols.
• It's stateless web service, which means that requests don't store client context over the servers and requests are independent of each other.
• It uses limited constraints and resources to communicate.
• Rest is simple and easy to learn.
• Uses HTTP and CRUD Operations.
• Supports many other data formats like : XML, JSON, Text etc.
• Uses less bandwidth due to small size of request and response.
• Can store cache to become more efficient.
• The interface is designed around resources that are identified by URLs.

Soap web service

• Soap stands for simple object access protocol.
• It actually a W3C web-service, people generally call it soap web service instead of W3C web service.
• It uses W3C web service architectural design, Soap Protocol and WSDL(web service description language).
• It has built-in stateful operations.
• It is slightly more secure than REST as it setup a formal contract between API and consumer using WSDL.
• The request and response have a Envelope structure which contains headers, body and other related information.
• It uses more bandwidth due to large size of the request and response body.
• It supports only XML for content.

Preferable application for Rest and Soap API

• Developing a public API : When developing a public API one should consider using REST API, as it will be more faster and efficient then SOAP API.
• Banking service or Enterprise service : Though most people have moved to REST, still there are people using SOAP API mainly for Banking service due to its security parameters OR in B2B applications because you can define a "data contract" with it.

Summary

Overall, REST is simpler to develop because it leverages the web, which is already in place, and the degree of freedom is limited (fewer choices to make, so simpler). SOAP offers several alternatives and is also slightly more difficult to develop, but offers more alternatives and areas to work.