SOAP vs. REST: A Look at Two Different API Styles

An API (application programming interface) allows two or more web applications to communicate and exchange data. For instance, e-commerce websites can connect to a payment processing API like Stripe to manage their online transactions.

APIs connect two pieces of software and act as the basis for communication in most modern applications. They allow us to streamline IT architectures, automate marketing workflows, and make it easier to share data sets.

When talking about API architectures, it’s common to compare SOAP vs REST, two of the most popular API paradigms. Although both facilitate communication between different applications, they’re inherently different technologies with unique characteristics.

Keep reading to understand the main difference between REST API and SOAP protocol and how these APIs fit different use cases.

What is an API?

REST, which stands for representational state transfer, is an essential API in web services. It uses the HTTP protocol and URIs (uniform resource identifiers) to facilitate communication between different platforms.

REST APIs have a handful of important characteristics that define their functionality and usage:

• Simplicity. REST APIs rely on HTTP protocols with straightforward methods for communication and data exchange.
• Client-server communication. Servers send data to client applications and receive feedback.
• Uniform interface. REST APIs operate the same way using a uniform interface, regardless of their size.
• Web optimization. Using the JSON data format makes it compatible with browsers.
• Performance and scalability. REST is known for excellent performance and scalability, but can have limitations addressed by other technologies like GraphQL.

Key components

Why use a REST API

REST APIs offer numerous advantages for software development and web services:

• Scalability. REST APIs are designed to handle a large number of clients and requests efficiently, making them ideal for scalable applications.
• Browser compatibility. Using JSON as the data format ensures broad compatibility across different browsers and platforms.
• Simplified security. REST APIs can leverage standard HTTP security measures, reducing the complexity of implementing custom security protocols.
• Enhanced discoverability. REST APIs are highly discoverable, making them user-friendly for developers. This allows for quick exploration and understanding of available resources and their corresponding URLs.
• Stateless nature. The stateless design of REST APIs improves performance and simplifies server-side operations.
• Flexible endpoints. REST APIs support multiple endpoints, allowing for modular and organized API design.
• Versatile HTTP methods. Utilizing various HTTP methods like GET, POST, PUT, and DELETE enables a wide range of operations.
• Language agnostic. REST APIs can be easily developed and consumed in various programming languages.
• Lightweight data transfer. REST APIs typically use JSON, which is more lightweight than XML, leading to faster data transfer and processing.
• Ideal for microservices. REST APIs are well-suited for building microservices architectures and developing loosely coupled systems.
• Caching capability. REST APIs can leverage HTTP caching mechanisms, improving performance for frequently accessed resources.

By leveraging these features, REST APIs provide a flexible, efficient, and widely adopted solution for modern web and mobile application development.

What is SOAP?

SOAP, which stands for simple object access protocol, is a more advanced API protocol compared to REST APIs, specifically due to how messages are sent and how it handles security. Though these in-built features add an extra layer of complexity, they can be worth it for organizations looking for robust security and ACID (atomicity, consistency, isolation, and durability) compliance.

While SOAP APIs can be used in simple web services scenarios, their robust features and enhanced security are better suited to enterprise-type situations.

Key components

Why use a SOAP API

Reasons you may want to develop an application with a SOAP API include:

• SOAP has much tighter security. In addition to SSL support, WS-Security is a built-in standard that gives SOAP web services enterprise-level security features.
• Successful/retry logic for reliable messaging functionality. REST APIs lack a standardized messaging system and mainly handle communication failures by retrying various requests. On the other hand, SOAP APIs have built-in retry logic, allowing them to handle errors more effectively and provide better reliability.
• SOAP supports ACID compliance. SOAP facilitates better ACID compliance than REST APIs. This leads to fewer anomalies and promotes database integrity by ensuring all transactions adhere to stipulated principles. ACID compliance is quite useful, especially when handling financial or sensitive information.

SOAP vs. REST example

To better grasp the practical differences between SOAP and REST, we created an example of how the same operation could be performed using the two technologies. In the example, we’re making a request for user details.

SOAP example

‍

--CODE language-markup line-numbers--
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:sch="http://www.soapexample.com/xml/users">
<soapenv:Header/>
<soapenv:Body>
<sch:UserDetailsRequest>
<sch:name>John</sch:name>
</sch:UserDetailsRequest>
</soapenv:Body>
</soapenv:Envelope>

‍

The response, just like the request, consists of a SOAP envelope and a SOAP body. In this case, the SOAP body represents the requested user data.

‍

--CODE language-markup line-numbers--
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
<soapenv:Header/>
<soapenv:Body>
<ns2:UserDetailsResponse xmlns:ns2="http://www.soapexample.com/xml/users">
<ns2:User>
<ns2:name>John</ns2:name>
<ns2:age>5</ns2:age>
<ns2:address>Greenville</ns2:address>
</ns2:User
</ns2:UserDetailsResponse>
</soapenv:Body>
</soapenv:Envelope>

‍

REST example

Using REST APIs can be called with all of the HTTP verbs. To get a resource, a GET request is used. In other words,  REST APIs can accept GET parameters from an URI while a SOAP request can only hold a user’s name in the body.

An example would be: GET https://restexample.com/users?name=John

--CODE language-markup line-numbers--
{
"name": "John",
"age": 5,
"address": "Greenville"
}

‍

SOAP vs. REST: The key differences

Below we’ll look at some of the key differences between the two paradigms.

SOAP is a protocol, whereas REST is an architectural style

SOAP uses a service interface to expose certain aspects of an application’s business logic, whereas REST relies on URIs. While SOAP APIs are designed after the functions that the API exposes, REST APIs are designed after the data.

To illustrate, a SOAP API that allows other applications to create users will feature a “CreateUser” function included in the SOAP body. On the other hand, a REST API will use a POST request via a URL to create a user and expose existing users via a GET request.

REST APIs access a resource for data (a URI); SOAP APIs perform an operation

REST is an architecture that’s more data-driven, while SOAP is a standardized protocol for transferring structured information that’s more function-driven. REST can support a wide variety of data formats, including JSON, XML, HTML, and plain text—leading to greater browser compatibility.

SOAP APIs are limited to using XML and the format including the SOAP envelope, header, and body, as we saw in the example above. REST APIs are, however, format agnostic. While the most common format is JSON, formats such as XML, plain text, and XML are also valid for REST APIs.

‍Security is handled differently

SOAP uses the WS-Security protocol, which is more efficient and robust compared to SSL, and can be easily integrated into other enterprise-level security tools. Nevertheless, both SOAP and REST can use SSL to enhance end-to-end security. REST APIs can even use the more secure HTTP protocol—HTTPS.

While both SOAP and REST APIs can encrypt their communication using HTTPS and SSL, the additional layer of WS-Security provided by SOAP acts on the message level to make sure that the content of a message can be read by the right server and also the right process on the server.

SOAP requires more bandwidth, whereas REST requires fewer resources (depending on the API)

There’s a little more overhead with SOAP out of the gate due to the larger payload size. Since REST is primarily applied in web services, it's more lightweight, making it a preferred choice for many web developers.

As shown in the SOAP example (in the previous section), SOAP requests typically hold more data compared to REST requests. This means more bandwidth will be consumed when communicating with a SOAP API. This can have an impact on systems with large amounts of traffic.

REST calls can be cached, while SOAP-based calls cannot be cached

Data can be marked as cacheable, which means it can be reused by the browser later without initiating another request back to the server. This saves time and resources. Since all SOAP requests are sent using a POST request, and POST requests are considered non-idempotent (meaning they change resources on a server) by the HTTP standard, responses will not be cached at the HTTP level.

REST APIs do not have this limitation, but you still need to implement the caching mechanisms yourself if you want to use caching. Caching is a key functionality when performance and scalability come into play.

APIs manage an app’s payload, and REST and SOAP handle this differently

Applications transmit data, known as payloads, over the internet. Large payloads demand more resources for transmission and processing. Understanding how different API architectures manage these payloads is crucial for efficient application design.

SOAP APIs are characterized by a strict communication contract, which often necessitates specific client-side plugins and coding to access the underlying API resources. This tight coupling with the server implies a lower level of abstraction in SOAP APIs. The stringent requirements of SOAP for communication can also make it challenging to implement changes or updates.

In contrast, REST APIs employ HTTP requests and the JSON data format to streamline payload size, enhancing application loading speeds. REST's architecture offers a higher level of abstraction, allowing for more straightforward updates and modifications without deep client-side knowledge of the API. This flexibility is a distinguishing feature of REST compared to SOAP.

From a development perspective, interfacing with a SOAP API often requires additional third-party libraries, while REST APIs typically only need the built-in HTTP request libraries of a programming language. This distinction highlights the differing levels of complexity and control in SOAP and REST, impacting both user experience and development approach.

Advanced features and specifications in SOAP and REST

Both SOAP and REST APIs have distinct features and authentication methods. We compare them below.

Protocol Features

SOAP uses advanced features to support complex operations and ensure reliable communication:

• Web Services Description Language (WSDL)some text
  • WSDL is an XML format for describing web services.
  • It highlights the services offered by a web service provider.
  • WSDL describes the format and type of messages shared between parties.
  • It promotes compatibility and interoperability across different systems.
    
    
• WS-Standardssome text
  • WS-Standards are built on top of the SOAP protocol to improve safety and reliability.
  • WS-Security describes rules for governing data integrity, encryption, authorization, and authentication.
  • WS-ReliableMessaging ensures that messages are delivered to the correct channels.
  • WS-Policy is responsible for defining the capabilities and constraints of different web services.

REST relies on simpler, more flexible features:

• Standard HTTP methods (GET, POST, PUT, DELETE)
• HTTP status codes for error handling
• Multiple data format support, with JSON being the most common
• URL structure for resource identification and manipulation

Authentication Methods

SOAP primarily uses the WS-Security standard, which includes:

• Security tokens
• XML digital signature
• XML encryption
• X.509 certificates for securing internet communications

REST APIs employ more flexible security measures, including:

• API keys
• OAuth 2.0
• Token-based authentication
• Basic HTTP authentication (username and password)

SOAP and REST alternatives

While SOAP and REST have been the primary choices for building APIs during the last decades, other alternatives are becoming increasingly common.

JSON

JSON (JavaScript object notation) is an open standard file format used to transmit data objects between many applications. It is a lightweight format to store and transfer data and is often used when sending data from a server to a web page. The simplicity and speedy transmission of JSON make it a viable alternative in many situations.

gRPC

gRPC (remote procedure call or RPC) is an open-source system developed by Google that uses HTTP/2. It is commonly used to provide a connection to different applications in a microservices architecture, and it allows mobile devices to communicate with backend services.

gRPC's advantages include lighter messages than JSON, high performance, built-in code generation, and support for more connection options, such as streaming data.

Falcor

Developed by Netflix, Falcor is a JavaScript library that assists in data fetching. It allows you to retrieve data from different sources and combine it into a single model. As a result, you can more easily pass data through different UI components and display it to users.

Falcor also supports client-side caching, meaning you can retrieve values from the local storage instead of making random network calls—which can otherwise be time-consuming and resource-intensive.

GraphQL

GraphQL is a query language used to efficiently load data from a server to a client. Created by Facebook, this relatively new technology supports reading, writing, and subscribing to changes to data, and GraphQL servers are available for languages like JavaScript, Python, C++, and more.

Just like REST, GraphQL communicates using HTTP and uses the JSON data format. One of the key differences and benefits is the possibility to specify the data you want to be returned from the server in one API call.

For example, if we want to fetch a customer, a customer order, and the order’s shipment status using REST, we would have to conduct separate HTTP requests for each piece of data. With GraphQL, we can fetch everything using one request, which eliminates the HTTP overhead for each call. It’s the reason companies like PayPal support GraphQL in addition to REST.

Practical applications

REST and SOAP have numerous use cases. Here’s how different companies are using these API technologies in their operations:

• X (formerly Twitter) uses a REST API to allow developers to manage their tweets, direct messages, and other data types.
• eBay offers a Trade API that uses REST fundamentals for creating and managing products.
• Optimizely supports both REST and SOAP APIs for integrating their project management tool with a PHP client.
• Salesforce uses a SOAP API to allow businesses to integrate its customer relationship model into their applications.

Apart from companies, SOAP and REST APIs are also featured in different operating systems. For starters, Windows uses SOAP APIs to connect users with external applications like Azure and SharePoint. Windows, MacOS, and Linux also use REST APIs to allow users to access underlying system resources and perform functions like creating user accounts and passwords.

Which API should you choose for your project?

For the most part, when it comes to APIs for web services, developers tend to prefer the RESTful architecture. However, the SOAP path is a better choice for an enterprise app that’s backed by more resources, needs super-tight security, and has more requirements.

Additional advantages in choosing the REST API include:

• Lightweight communication using HTTP and small payloads, such as in the JSON data format
• Fewer restrictions on third-party dependencies on the client-side
• Enables the use of effective caching

There are, however, cases when SOAP might be your first choice, including:

• Enterprise-level requirements on security
• Need to integrate with legacy systems already using SOAP
• Compliance with ACID transactions or support for built-in retry mechanisms

No matter which technology you use, the most important part of building a good API is designing it using best practices to make it easy to use and understand for clients. A well-designed API can greatly increase your delivery speed and future-proof your technology stack.

Future trends and evolving technologies in APIs

SOAP and REST are robust API styles that allow computer systems to communicate. However, with continuous innovation, new technologies are constantly emerging and redefining the field of API development.

GraphQL

GraphQL is an emerging technology that allows developers to retrieve only the data they need for specific functions. It eliminates the risk of over-fetching or under-fetching data, leading to improved efficiency and performance.

API Gateways

API gateways are becoming increasingly popular, especially for managing routing requests. These gateways are robust and convenient because they come with numerous out-of-the-box tools for managing an entire API lifecycle.

Public APIs

Public APIs are gaining importance in the following ways:

• Integration. They allow developers to quickly integrate crucial functionalities into their applications rather than creating them from scratch, saving time and increasing productivity.
• Security. With tight data protection regulations being implemented across the industry, public APIs are increasingly adopting advanced security measures like encryption and tokenization to keep user data safe.
• Asynchronous architecture. Many public APIs are adopting asynchronous architecture, allowing them to respond quickly to user events with real-time data.
• Microservices support. As many companies shift to microservices, public APIs are emerging as valuable data sources for context-specific information.

Find help with SOAP and REST APIs on Upwork

Developing SOAP or REST APIs demands a specific set of technical skills that takes time to master. Upwork can connect you with SOAP freelancers, REST freelancers, and API developers to help you create robust APIs.

If you’re an expert looking for work, start your search on Upwork. With different projects being posted regularly, you can find jobs in SOAP, REST, and API development and earn extra income. Get started today!

‍

Upwork is not affiliated with and does not sponsor or endorse any of the tools or services discussed in this article. These tools and services are provided only as potential options, and each reader and company should take the time needed to adequately analyze and determine the tools or services that would best fit their specific needs and situation.