SOAP and REST are two internet data exchange mechanisms. For example, imagine that your internal accounts system shares data with your customer’s accounting system to automate invoicing tasks. The two applications share data by using an API that defines communication rules. SOAP and REST are two different approaches to API design. The SOAP approach is highly structured and uses XML data format. REST is more flexible and allows applications to exchange data in multiple formats.
To build applications, you can use many different programming languages, architectures, and platforms. It’s challenging to share data between such varied technologies because they have different data formats. Both SOAP and REST emerged in an attempt to solve this problem.
You can use SOAP and REST to build APIs or communication points between diverse applications. The terms web service and API are used interchangeably. However, APIs are the broader category. Web services are a special type of API.
Here are other similarities between SOAP and REST:
You can use either SOAP or REST to build secure, scalable, and fault-tolerant distributed systems.
Before choosing between SOAP and REST, consider your scenarios and your API users’ requirements. The following criteria are worth considering.
Modern applications like mobile apps and hybrid applications work better with REST APIs. REST gives you the scalability and flexibility to design applications using modern architecture patterns like microservices and containers. However, if you need to integrate or extend legacy systems that already have SOAP APIs, you may be better off continuing with SOAP.
Public APIs have lower security requirements and demand greater flexibility so anyone can interact with them. So, REST is a better choice when you build public APIs. Conversely, some private APIs for internal enterprise requirements (like data reporting for compliance) may benefit from the tighter security measures in WS-Security of SOAP.
Do your API users require stringent consistency and data integrity across a chain of transactions? For instance, finance transactions require an entire batch of data updates to fail if even one update fails.
SOAP has built-in compliance for atomicity, consistency, isolation, and durability (ACID). And SOAP may be better suited for high data integrity requirements. In this case, REST APIs may require additional software modules to enforce the state at the server or database level.
SOAP is an older technology that requires a strict communication contract between systems. New web service standards have been added over time to accommodate technology changes, but they create additional overheads. REST was developed after SOAP and inherently solves many of its shortcomings. REST web services are also called RESTful web services.
SOAP is a protocol that defines rigid communication rules. It has several associated standards that control every aspect of the data exchange. For example, here are some standards SOAP uses:
When you send a request to a SOAP API, you must wrap your HTTP request in a SOAP envelope. This is a data structure that modifies the underlying HTTP content with SOAP request requirements. Due to the envelope, you can also send requests to SOAP web services with other transport protocols, like TCP or Internet Control Message Protocol (ICMP). However, SOAP APIs and SOAP web services always return XML documents in their responses.
REST is a software architectural style that imposes six conditions on how an API should work. These are the six principles REST APIs follow:
You send REST requests using HTTP verbs like GET and POST. Rest API responses are typically in JSON but can also be of a different data format.
SOAP is a protocol, while REST is an architectural style. This creates significant differences in how SOAP APIs and REST APIs behave.
The SOAP API exposes functions or operations, while REST APIs are data-driven. For example, consider an application with employee data that other applications can manipulate. The application’s SOAP API could expose a function called CreateEmployee. To create an employee, you would specify the function name in your SOAP message when sending a request.
However, the application’s REST API could expose a URL called /employees, and a POST request to that URL would create a new employee record.
SOAP APIs are rigid and only allow XML messaging between applications. The application server also has to maintain the state of each client. This means it has to remember all previous requests when processing a new request.
REST is more flexible and allows applications to transfer data as plain text, HTML, XML, and JSON. REST is also stateless, so the REST API treats every new request independently of previous requests.
SOAP messages are larger and more complex, which makes them slower to transmit and process. This can increase page load times.
REST is faster and more efficient than SOAP due to the smaller message sizes of REST. REST responses are also cacheable, so the server can store frequently accessed data in a cache for even shorter page load times.
The SOAP protocol requires applications to store the state between requests, which increases bandwidth and memory requirements. As a result, it makes applications expensive and challenging to scale.
Unlike SOAP, REST permits stateless and layered architecture, which makes it more scalable. For example, the application server can pass the request to other servers or allow an intermediary (like a content delivery network) to handle it.
SOAP requires an additional layer of WS-Security to work with HTTPS. WS-Security uses additional header content to ensure only the designated process in the specified server reads the SOAP message content. This adds communication overheads and negatively impacts performance.
REST supports HTTPS without additional overheads.
SOAP has error handling logic built into it, and it provides more reliability. On the other hand, REST requires you to try again in case of communication failures, and it’s less reliable.
| SOAP | REST | |
| Stands for | Simple Object Access Protocol | Representational State Transfer |
| What is it? | SOAP is a protocol for communication between applications | REST is an architecture style for designing communication interfaces. |
| Design | SOAP API exposes the operation. | REST API exposes the data. |
| Transport Protocol | SOAP is independent and can work with any transport protocol. | REST works only with HTTPS. |
| Data format | SOAP supports only XML data exchange. | REST supports XML, JSON, plain text, HTML. |
| Performance | SOAP messages are larger, which makes communication slower. | REST has faster performance due to smaller messages and caching support. |
| Scalability | SOAP is difficult to scale. The server maintains state by storing all previous messages exchanged with a client. | REST is easy to scale. It’s stateless, so every message is processed independently of previous messages. |
| Security | SOAP supports encryption with additional overheads. | REST supports encryption without affecting performance. |
| Use case | SOAP is useful in legacy applications and private APIs. | REST is useful in modern applications and public APIs. |
