What’s the Difference Between SOAP and REST?
An API (application programming interface) is an information gateway that helps facilitate seamless communication between apps, software, and services. When a team starts to discuss how to create a public API to link their software to other popular programs, one question often comes up: should the team use SOAP or REST?
While REST and SOAP are both related to the design and development of APIs, considering the two isn’t an “apples to apples” comparison: SOAP is a protocol while REST is an architectural style. Let’s take a closer look at these two API styles.
What is REST?
REST (short for Representational State Transfer) is an architectural style that facilitates communication between computer systems across a network.
The main idea behind REST is to provide a uniform interface between components by enforcing certain design constraints so that there is an official procedure for transferring data between the back ends of different software components.
What does that mean in plain English?
Think about the last time you ordered coffee at your local cafe. You’re not allowed behind the counter, but you can use the menu to place a custom order with the barista. In this analogy, the menu is like API documentation, which provides a list of available requests you can make to an API. The kitchen is like the computer server, and the ingredients that make up your order (e.g., coffee, milk, and sugar) are like the data resources stored on the server, which must be assembled into a proper response. The barista is the API that fulfills your order.
This request-response architecture is one of the foundational architectures behind the World Wide Web which uses HTTP(S) as its primary messaging protocol. Just as there’s more than one way to layout a restaurant or cafe, there’s more than one way to design an API. But to actually understand the design constraints that make an API RESTful, there’s no avoiding the technical details. Check out this handy beginner’s guide to REST APIs for a more in-depth explanation.
What is SOAP?
SOAP is short for Simple Object Access Protocol. Unlike REST, which is a broad architectural style, SOAP is a messaging protocol specification, a specific set of strict standards for how messages can be sent. It’s entirely possible to design your API in broad strokes with REST and use SOAP as your messaging protocol. Here’s a look at SOAP’s core features:
- Built-in ACID (Atomicity, Consistency, Isolation, Durability) compliance
- Tighter security with WS-Security and SSL support
- Built-in retry logic for reliable messaging
- More ideal for enterprise/desktop software than web services
SOAP emphasizes extensibility, neutrality, and independence. While it uses XML exclusively as its message format, it can be used with other application layer protocols such as HTTP and SMTP. Because SOAP is more secure, it is particularly suited to projects where security is a priority, such as mobile banking apps or enterprise software.
Key differences between REST and SOAP
The main differences between REST and SOAP have been summarised in the table below:
The general consensus: use REST unless you have a compelling reason to use SOAP. It goes back to how REST is an architectural style while SOAP is a messaging protocol specification. REST covers the broad scope of how other software components will retrieve information from your servers, while SOAP specifies granular details about the actual format of that data.
The main takeaway is to use SOAP if you need the enhanced security from WS-Security, are using XML as your data type, and/or require ACID compliance. Otherwise, it’s easier to work with REST over HTTP(S) for most API needs.