API Rest VS SOAP -Top 15 Key Differences (Testers Edition)

January 5, 2024Priyanka
API Rest vs SoapUI

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The Application Programming Interface (API) is a way for two or more applications to communicate with each other. It is an interface that offers service to other pieces of software or applications. The API REST and SOAP are two methods of exchanging data through API. They both have unique features and are built for specific purposes. Most of the APIs developed today are REST-based as it is easy to build and serve most of the needs. The SOAP is still a feasible option for specific use cases. Let’s understand the API REST vs SOAP in detail.

Difference Between SOAP and REST

An API uses the API specifications, which define the characteristics of the API. The main difference between SOAP and REST is a protocol ; while REST can be defined as architectural style. REST API can use the SOAP protocol or HTTP protocol. However, the SOAP cannot use the REST API.

What is REST

REST (Representational State Transfer)  is the type of architectural pattern adopted widely for modern web-based application development. It can administer the key application components like files, media components, or objects. The REST uses the API-ready approach. It uses the HTTP protocol for communication. You can also use HTTP verbs like GET, PUT, POST, etc. To perform the operations using the REST API. It supports different types of data formats for communications such as XML, JSON, plain text, or any custom formats.

What is SOAP?

SOAP means Simple Object Access Protocol and is an API protocol designed with the intention of security and consistency in the data exchange process.  It uses the XML data format for communications and can only be used for web services. It can consume more bandwidth as SOAP messages hold a huge chunk of data.

SOAP and REST Examples

SOAP and REST use different formats for communications. The SOAP uses XML and the REST can use JSON or any customized formats. Below is an example of these two

Example of SOAP

The SOAP requests are delivered in envelopes, these envelopes hold crucial information for processing the request. The header and body attributes are key parts.

<?xml version="1.0"?>
<m:Trans xmlns:m="https://www.example.com/transaction/"
  <m:GetPrices xmlns:m="https://www.example.com/priceinformation">

Example of REST

The REST API looks just like your website URL as it communicates using the HTTP. You just have to send the request with parameters to fetch the details.

GET https://example.com/users?name=david

Once you send the above request you will get the response in predefined format. In our case it is JSON

{ “name”: “David”, “userType”: “Gold”, “address”: “Bangalore” }

When to use SOAP vs REST?

As mentioned earlier both SOAP and REST are built for specific use cases. Let’s understand when to use what.

When to use REST?

  • Limited bandwidth

REST consumes significantly limited bandwidth compared to SOAP, so if there is a resource crunch then the REST is the best choice.

  • No need to maintain a state

By definition, REST is stateless, which means it doesn’t remember previous request details. So if the request doesn’t need the state then the REST is a powerful choice.

  • Caching huge requests

If your application involves caching a large number of requests/responses with accuracy then you should consider REST. This will also improve the performance, and it is supported by all means.

  • Simpler and Easy

REST is much simpler compared to SOAP; it is easy to develop, implement and use. This is one of the reasons why REST is very popular and used without even a second thought.

When to use SOAP

  • Security 

When there is a need for additional level security SOAP is the most trusted protocol. SOAP 1.2 provides a lot of additional levels of security features compared to REST.

  • Stateful

Unlike REST the SOAP is stateful which means it remembers the previous request. If you need to perform the stateful operation using an API, you can use SOAP.

  • Asynchronous operations

An asynchronous operation is time-specific. SOAP supports additional protocols for communication. The SOAP is best fit when there is a requirement for asynchronous operations.

  • Formal communication protocol

SOAP can be used for official communication. The SOAP 1.2 offers a wide range of specifications to communicate between client and server.

Converting SOAP to REST

Since modern web development uses the REST you might have to convert an existing SOAP API to REST, though converting APIs is not easy we can achieve them.

Locate the API

First, you need to locate the API to convert. Start by understanding what it does and how it is implemented using the SOAP.

Define the WSDL URI

WSDL is Web Services Description Language, the REST relies on WSDL. You need to define the WSDL URI for your API to convert from SOAP to REST

Convert the Implementation

Once you define the WSDL URI, look for the SOAP implementation and convert them as per REST specifications. By following the REST specifications documentation you should be able to write the implementation and utilize them.

Can REST use SOAP?

Yes, REST can use SOAP. The SOAP is a protocol, and REST API can utilize the SOAP protocol.  REST is an architectural practice hence it can utilize any protocol. However the other way is not true, that is SOAP cannot utilize the REST.

Is SOAP more secure than REST?

API security is important while designing the interface. Both REST and SOAP offer security. However, there is no argument that SOAP is more secure than the REST. Though SOAP 1.2 offers an additional layer of security, Thus, it is considered more secure.

Is REST API better than SOAP?

REST API is easy to implement and easy to use. Using the REST API is just like a web URL.  It uses HTTP verbs such as GET, POST, and PUT for its operations. REST can use any format body for communication such as JSON, plain text, etc. REST doesn’t compromise performance even if there is a huge number of requests. So, the REST is better compared to SOAP.

 Why is REST Faster Than SOAP Web Services?

The REST supports caching, but the SOAP message holds a huge chunk of information so it uses more bandwidth and is comparatively slower than the REST.

Benefits of REST Over SOAP

  • REST supports a wide range of data formats and REST can use SOAP. The SOAP has only a limited data format. Only the .xml format can be used for SOAP.
  • All major browser clients support REST, and is easy to use and maintain
  • The REST supports the caching of information, which makes REST faster even with a large number of requests.
  • When REST is used with JSON, it makes complex data exchange more simple to use
  • REST utilizes less bandwidth and great performance
  • REST makes applications simple and it’s easy to implement, whereas SOAP looks more complicated in comparison with REST

Benefits Of SOAP Over REST

  • SOAP supports a built-in retry option. In case the request exchange fails it automatically retries failed communication. However, in the case of REST, it has to be rewritten.
  • SOAP enforces strict standards with rules. Hence SOAP is known as the more reliable and standard protocol for API design. The REST only talks about recommendations, no strict enforcement.
  • The SOAP offers additional layers of security, which will be helpful to achieve greater security in comparison with REST
  • The SOAP is compatible with more extensions than the REST. It works very well with WS-RM and WS-coordination, WS-A, and other specifications as recommended by the W3C.

What are the Similarities between SOAP and REST?

As we discussed in previous sections, SOAP and REST are the most popular API designing techniques. Though many are choosing the REST, as it is easy to use. The SOAP is still a popular and standard choice for many organizations. Let’s look at the similarities between SOAP and REST

  • The SOAP and REST both help to connect between two systems and interact with each other.
  • Both SOAP and REST can make use of HTTP protocols efficiently to provide the expected outcome.
  • Both can understand the XML, and communicate with systems with XML data format
  • They both provide security and encryption using the SSL/TLS layer for security
  • Both describe the rules, protocols, and standards on how applications can interact with each other, send the data, and respond to them.

REST vs. SOAP: What’s the Difference?

The REST and SOAP have differences, and understanding the key differences which helps you to choose the best API specification according to your needs. Let’s try to analyze their key differences.

Stands for SOAP is a Simple Object Access ProtocolRepresentational State Transfer
DesignSOAP exposes the functions and/or operationsREST is data-driven
FlexibilitySOAP only supports XML data format to exchangeREST is flexible; it allows different types of data formats for communications such as plain text, HTML, XML, and JSON.
PerformanceThe performance of SOAP is comparatively slowREST is faster and more efficient
Bandwidth and SpeedThe SOAP messages are more complex and larger hence they utilize more bandwidth and are slowerThe REST is faster as it supports caching, and it utilizes less bandwidth for its operations
ScalabilityThe SOAP is stateful, which requires more memory and bandwidth so it makes the application more complex and expensiveThe REST is stateless and more scalable as per requirement
SecurityThe SOAP is more secure. The SOAP 1.2 offers additional layers of securityThe REST is also secured however, unlike SOAP it doesn’t offer an additional layer of security
ReliabilitySOAP has in-built error handling hence, it’s more reliableThe REST requires the implementation of  a retry logic hence, it is less reliable
Transfer protocolHTTP, UDP, SMP, etc.HTTPS
How it is builtTechnically the SOAP is built around RPC(Remote Procedure Call)The REST is resource-based
Use caseSOAP is mostly used for legacy applications and private APIsREST is used for modern applications and public endpoints

REST vs SOAP: Choosing the Right Protocol for your Web APIs

There is no golden rule to choose the right type of API. Considering the facts, modern applications are designed with REST but it doesn’t mean that SOAP doesn’t exist. There are still many organizations using the SOAP API’s for the communications. In short, if you need stateless, better performance for huge requests, building applications around modern architecture, and your applications don’t require any other protocol than HTTP/HTTPS, use the REST API. If you are more concerned about security, statefulness and if some part of your application already uses SOAP and you have no plan to migrate, requires more reliable communication, and performance is not a factor then go for SOAP API

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Both SOAP and REST are popular and widely used. It is also true that modern applications are extensively built with REST APIs as it is simpler, offers more speed, and less data. Regardless of whatever API you choose, API Testing is the most critical part of your development cycle and you cannot skip that. While you choose the simple and easy way to develop an API, it is also important to choose the more simple and easy-to-use tool for testing. Testsigma is one such tool that offers API testing without writing a code. Testsigma offers its SaaS-based testing where the team can collaboratively work without installing any desktop client.

Frequently Asked Questions

What is the difference between SOAP API and JSON API?

The SOAP API is limited to XML data format for communication, while REST offers JSON as the primary data format for communication. Hence REST can also be called JSON API.

What are the alternatives to SOAP and REST?

GraphQL and gRPC are considered alternatives for SOAP and REST APIs. There are a few more alternatives that are less used such as WebSockets, MQTT, EDA, etc.

Why is REST preferred over SOAP? 

REST is simple, provides better performance and it has caching support. Hence it is more preferred over SOAP.

What is the difference between REST API and Postman API?

The REST API is the API standard whereas the Postman is the tool for building and testing the API. The Postman platform is often used as Postman API


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