A Guide to the Most Popular Types of APIs: REST, SOAP, GraphQL, and gRPC
Tags: webdev, beginners, api, computerscience
Published: 2022-11-26 15:07:56

APIs are the most important component of the modern-day software development process, helping applications and services communicate and transfer crucial information. 

However, with the advancements in the field, now there are various choices to go with: REST, SOAP, GraphQL, or gRPC. That means whether you are an application architect or a backend developer, it’s essential that you understand which APIs are the best suited to particular applications.

Each API type has its unique architecture, which evolved in response to the needs of the time. And, as technology has evolved and our relationship with technology has altered, we've seen APIs arise to cover new gaps and serve new uses.

In this article, we’ll look at how SOAP, REST, GraphQL, and gRPC APIs compare to each other to give you a sense of their pros and cons, common use cases, and other considerations when you’re choosing the best one for your needs.

## REST APIs
REpresentational State Transfer (REST) is a software architectural style for developing APIs to provide a simple, uniform interface. These can be used to make data, content, algorithms, media, and other digital resources accessible via web URLs, allowing them to be consumed via the web, mobile, and device applications. They allow data exchange in simple formats such as JSON and XML.

REST APIs adhere to the following six specific architectural constraints:

1. A uniform interface
2. Completely stateless
3. Native caching
4. Client-server architecture
5. A layered system
6. The ability to provide executable code to the client

Here’s an example of a REST API message:

```js
{
  "car": {
    "vin": "KNDJT2A23A7703818",
    "make": "kia",
    "model": "soul",
    "year": 2010,
    "links": {
      "service": "/cars/KNDJT2A23A7703818/service",
      "sell": "/cars/KNDJT2A23A7703818/sell",
      "clean": "/cars/KNDJT2A23A7703818/sell"
    }
  }
}
```


### Pros
- REST APIs are based on the HTTP protocol, which means they are format-agnostic, allowing you to utilize XML, JSON, HTML, and other formats. This makes REST APIs quick and lightweight, which is essential for mobile app development, internet of things devices, and other applications.

- REST APIs can be discovered easily from the URL, thus, they are very easy for the developers to test and integrate with their applications.

- REST APIs are stateless, hence, they are very flexible to use as well as highly scalable as per the use case.

- These APIs can be developed in Python, JavaScript (Node.js), Ruby, C#, and a variety of other languages, making them more accessible to most developers.

### Cons
- One downside of RESTful APIs is the loss of the ability to maintain a state, such as within sessions. It may also be more challenging to utilize for novice developers.

- REST does impose any security thus, it is appropriate for public URLs, but it is not good for confidential data exchange between the client and the server. 

- There is no binding contract on the structure of communication. As a result, when it comes to execution, there is a lot of back and forth, which can lead to unnecessary frustration and bottlenecks.


You can use API Tester to [create and send your first REST API request](https://docs.apitester.org/api-tester-features#create-and-send-request) and see for yourself how it works.

## SOAP APIs
The Simple Object Access Protocol (SOAP) is a protocol for sharing information encoded in Extensible Markup Language (XML) between a client and an Internet-based operation or service. It can be used with various transport protocols such as HTTP, FTP, SMTP, etc. 

SOAP is commonly used in conjunction with the Web Service Description Language (WSDL). The importance of WSDL is that it allows developers and machines to analyze a web service that supports SOAP to learn about the nuances of information exchange over the network. Furthermore, the WSDL explains how to format the SOAP request and answer messages supported by the provided service. 

SOAP is utilized for enterprise-level web services requiring high security and complicated transactions. SOAP is frequently used in APIs for financial services, payment gateways, CRM software, identity management, and telephony services.

A SOAP message has a hierarchical structure, with the `<soap:Envelope>` as the root element. Three child elements can be added to the root element. These are the child elements `<soap:Header>`, `<soap:Body>`, and `<soap:Fault>`.

Here’s an example of a SOAP message:

```
POST /Quotation HTTP/1.0
Host: www.xyz.org
Content-Type: text/xml; charset = utf-8
Content-Length: nnn

<?xml version = "1.0"?>
<SOAP-ENV:Envelope
   xmlns:SOAP-ENV = "http://www.w3.org/2001/12/soap-envelope"
   SOAP-ENV:encodingStyle = "http://www.w3.org/2001/12/soap-encoding">

   <SOAP-ENV:Body xmlns:m = "http://www.xyz.org/quotations">
      <m:GetQuotation>
         <m:QuotationsName>MiscroSoft</m:QuotationsName>
      </m:GetQuotation>
   </SOAP-ENV:Body>
</SOAP-ENV:Envelope>
```

### Pros

- SOAP is completely programming language and processing platform agnostic because of the standardized format.
- SOAP APIs come with built-in native error handling, helping developers quickly identify and resolve problems.
- SOAP APIs are the best suited for transferring sensitive data to and fro such as financial data as its standardization allows a specific contract to be imposed in form of code throughout all of the APIs.
- Stateful operations are supported by SOAP and may be implemented using the WS-* (Web Services) Specifications, which are built on top of the basic XML and SOAP standards.

### Cons
- Because SOAP can only send messages as XML files, your SOAP API will be less performant, as XML is a more verbose format than JSON.
- SOAP API requests to your server consume more bandwidth and take longer to process the request and return the result to the client.
- SOAP client-server communication is based on WSDL (Web Service Description Language) contracts, implying a close connection. As a result, it is not suitable for loosely connected applications since you cannot avoid a contract between the client and the server.
- SOAP also has a steeper learning curve, is more difficult to develop, and cannot be tested in a web browser (as opposed to REST). SOAP requires you to construct contracts in WSDL, establish client stubs, adhere to tight requirements, and more. As a result, as a programmer, you will have less flexibility in choice.

API Tester supports [sending requests to SOAP APIs](https://docs.apitester.org/api-tester-features#soap-requests) and allows you to test your APIs without any effort in a quick and easy way. 

## GraphQL APIs
When Facebook created [GraphQL](https://graphql.org/), they required a robust data-fetching API that could perform all of Facebook's tasks while being straightforward and easy to learn and use by their product developers. GraphQL was created in order to rebuild Facebook's native mobile apps.

GraphQL is a query language. It returns a query in the form of a string, which is then submitted to a server. The server processes the query and delivers the response to the client in JSON format. 

GraphQL is a strongly typed language in which each level of a GraphQL query corresponds to a different type, and each type represents a different set of accessible fields. As a result, it is similar to SQL in that it offers informative error warnings prior to performing a query, hence the name.

GraphQL has a hierarchical structure in which relationships between objects are defined graphically. Every object type represents a component in this context, and every related field from one object type to another represents a component wrapping another component.

A simple GraphQL request looks like this:

```
{
  me {
    name
    friends {
        name
    }
  }
}
```

When migrating from a monolithic backend application to a microservice design, the GraphQL API may assist us in managing communication between numerous microservices by integrating them into a single GraphQL schema.

### Pros
- GraphQL is significantly faster than other communication APIs because it allows you to narrow down your request query by selecting only the data you wish to query. Thus, it resolves all over-fetching and under-fetching problems.

- Using GraphQL's API, we can integrate numerous platforms. It brings them together while masking their complexities. The GraphQL server is also used to retrieve data from existing systems and package it in GraphQL response format. This is especially useful for legacy infrastructures or third-party APIs that are massive in size and difficult to manage.

- When we send GraphQL queries to the server, the server responds in a simple, secure, and predictable format. As a result, it makes it easier for you to construct a customized query based on your needs. This makes GraphQL extremely simple to learn and use.

- At a higher component level, we can share the GraphQL fields used in many queries for reuse. This feature is known as fragments, and it allows you to obtain diverse data while maintaining the same schema field.

- Because the result set or returned data in GraphQL is highly particular to the client's query, it is quite straightforward and easy for the server to generalize it. When we add new product features or fields to the server, it has no effect on old clients. You can continue to utilize the older server without concern because server fields can be deprecated but still operate. This compatible procedure does not necessitate the use of an ever-increasing version number. As you can see, Facebook uses the same version of GraphQL API in all of its applications.

### Cons
- One downside is that queries always return an HTTP status code of 200, regardless of whether they were successful or not. If your query fails, your return JSON will include a top-level errors key containing error messages and a stack trace. This can make error handling considerably more difficult and add to the complexity of things like monitoring.
- It is more complicated to implement a simplified cache with GraphQL than to implement it in REST. 
- Rate-limiting is another issue with GraphQL. In REST API, you can easily write "we accept just this many requests in one day," but in GraphQL, this sort of statement is harder to convey.
- GraphQL is difficult to pick up without lots of training and experience. 

[GitHub’s GraphQL API](https://docs.apitester.org/guides/github-graphql-api-guide) is the most commonly used free developer API. [Create and run a GraphQL request](https://docs.apitester.org/api-tester-features#graphql) in API Tester within minutes and get started to explore more!

## gRPC
[gRPC Remote Procedure Call](https://grpc.io/) (gRPC) is a cross-platform, open-source, contract-based communication protocol that streamlines and controls interservice communication by providing a set of functions to external clients.

The 'g' at the beginning indicates that this is the most advanced version created by Google in 2015. On one side, a user will pick a remote process to run, serialize the required parameters, and then attach any additional information to the message. This is then transferred to the server, which communicates with the other application, decoding the message and performing the action. The original user is then given a result.

### Pros
- It is simple and straightforward, GET is used to fetch information and POST for everything else. 
- Functions are simple to add, and for lightweight payloads, overall performance is excellent. Thus, it is endlessly customizable due to the flexibility to define any type of function.

### Cons
- The fact that gRPC is strongly connected to the underlying system limits its reusability in many circumstances is where it falls short. Furthermore, no abstraction layer exists between the API and the real system functions, which raises security problems.

## How to Choose the Right API for Your Use?
As you might be able to guess from the above discussion, there is no “best” API type, each of the API types have its distinct characteristics that make them well suited for specific applications. However, the question still remains - how to find the one that works the best for you?

Here are some questions that can help you determine:

- Which programming language would you like to use?
- Which environment will you be developing in?
- What is the most important functionality for this API?
- What skills do you have on staff? What skills can you acquire?
- What resources have you set aside for this project?

Remember that you can always run a simple proof-of-concept with one or two types to test how they work. You can also use [API Tester](https://apitester.org/), an easy-to-use mobile app that helps you to test any API on your phone. 

## Conclusion
We hope this blog post was helpful in distinguishing between the most popular types of APIs. Each has a purpose, and when you make a deliberate and considered selection up front, you're well on your way to designing an API that is not just effective but also resource-conscious.