SOAP or Simple Object Access Protocol connects processes through HTTP (mostly!) and the XML data format. SOAP follows preset standards like a messaging structure, encoding rules, and conventions for procedure requests and responses.
SOAP and XML based Web Services aren’t dead yet. I don’t think they will be for quite a while because they are very common in large enterprises (government, banks, telecommunications, etc).
In B2B or service to service APIs with a reliable and fast connection there’s some advantages to using SOAP with languages and environments like C#.NET or Java that.
There is a lot of large software systems that still provide SOAP based APIs. For example, NetSuite and Salesforce still have SOAP based APIs. NetSuite’s SOAP based API is actually better than their REST based API.
What is replacing SOAP?
The emphasis today is more on RESTful HTTP Service (RESTful APIs), although there’s some companies transitioning to GraphQL.
In the article, API Style Choices you can read about some of the alternatives.
Should we still build new SOAP based APIs?
I personally wouldn’t, five years I might have considered it because the discoverability and WSDLs can be pretty spectacular.
Now a days, most web and mobile APIs are implemented using RESTful architectures because JSON is much more compressed and natively supported in web browsers. Parsing JSON data is usually a lot easier than XML data too. 😊
Also published on Medium.