Understand the differences between REST and SOAP APIs so you can pick the right approach to your API documentation.
Key takeaways:
REST APIs are simpler, more lightweight, and easier to use than SOAP APIs. They are also more flexible and can be used with a wider variety of programming languages and frameworks. However, SOAP APIs may be more appropriate for certain types of applications that require more advanced features such as message-level security or transaction support.
REST APIs and SOAP APIs have different documentation needs because of their differences in request and response structures, service description, and client libraries. The documentation for each type of API needs to be tailored to its specific characteristics and requirements.
What is a REST API?
A RESTful API is a web-based application programming interface (API) that follows the principles of Representational State Transfer (REST) architecture. It uses standard HTTP methods such as GET, POST, PUT, and DELETE to perform various operations on resources identified by unique URLs. RESTful APIs are stateless, meaning that each request contains all the necessary information to perform the operation, and the server does not store any client session information between requests. This allows for efficient and scalable communication between the client and server, making RESTful APIs a popular choice for building web services and applications.
If you're just getting started with REST APIs, check out Learn REST APIs.
What is SOAP API?
SOAP API stands for Simple Object Access Protocol Application Programming Interface. It is a protocol for exchanging structured data between applications over the internet, using the XML format. SOAP is a messaging protocol, where a client sends a request to a server and the server sends back a response. SOAP messages can be sent over a variety of transport protocols, such as HTTP, SMTP, or JMS. SOAP APIs typically use WSDL (Web Services Description Language) to describe the operations, messages, and endpoints of the API. SOAP APIs were widely used in the past for building distributed systems and web services, but they have become less popular in recent years due to the rise of RESTful APIs, which are simpler, more lightweight, and easier to use.
If you're just getting started with SOAP APIs, check out Programming Web Services with SOAP.
What are the major differences?
Major differences between REST APIs and SOAP APIs include:
Architectural style: REST (Representational State Transfer) is an architectural style for building web services, while SOAP (Simple Object Access Protocol) is a messaging protocol.
Data format: REST APIs typically use lightweight data formats such as JSON (JavaScript Object Notation) or XML (Extensible Markup Language), while SOAP APIs use XML exclusively.
Transport protocol: REST APIs can use a variety of transport protocols, such as HTTP, while SOAP APIs typically use HTTP or Simple Mail Transfer Protocol (SMTP).
Error handling: REST APIs use HTTP error codes to indicate errors, while SOAP APIs use a specific XML structure to convey error messages.
Service description: REST APIs typically use a human-readable description format such as Swagger or OpenAPI, while SOAP APIs use Web Services Description Language (WSDL).
State management: REST APIs are stateless, meaning that each request contains all the information needed to complete the request. In contrast, SOAP APIs can maintain state information between requests.
Payload size: REST APIs typically have smaller payloads than SOAP APIs due to their lightweight data formats.
REST APIs are simpler, more lightweight, and easier to use than SOAP APIs. They are also more flexible and can be used with a wider variety of programming languages and frameworks. However, SOAP APIs may be more appropriate for certain types of applications that require more advanced features such as message-level security or transaction support.
How does this impact developer documentation?
REST APIs and SOAP APIs have different architectural styles, data formats, and message protocols, which means that they have different documentation needs.
Here's why REST APIs and SOAP APIs need to be documented in different ways:
Request and response structures: REST APIs and SOAP APIs have different structures for their requests and responses. REST APIs typically use HTTP methods and status codes to specify the operations and results, while SOAP APIs use XML payloads with specific message structures. This means that the documentation for REST APIs needs to focus on the HTTP methods, URL structure, query parameters, and response codes, while the documentation for SOAP APIs needs to focus on the SOAP message structure, schema, and headers.
Service description: REST APIs typically use a machine-readable format such as OpenAPI or Swagger to describe their endpoints and operations, while SOAP APIs use WSDL (Web Services Description Language) to describe their messages and interfaces. This means that the documentation for REST APIs needs to include a description of the API schema, while the documentation for SOAP APIs needs to include a WSDL file that describes the service interfaces and message formats.
Client libraries and SDKs: REST APIs and SOAP APIs may have different requirements for client libraries and software development kits (SDKs). REST APIs may require libraries for handling JSON or XML payloads, while SOAP APIs may require libraries for handling SOAP messages and attachments. This means that the documentation for REST APIs needs to include information on how to use client libraries and SDKs for different programming languages, while the documentation for SOAP APIs needs to include information on how to generate client stubs and proxies from the WSDL file.
