What is a REST API (RESTful API)?

REST APIs offer a flexible method of interconnecting different software applications. They enable apps to securely exchange information over the web. Whenever you’re using an app which is retrieving information from another, it’s likely a REST API at work.

This article will explain how this technology works, its importance, challenges and best practices. We’ll also dive into its history to show you how it evolved over the years.

What’s an API?

API stands for Application Programming Interface. It is a set of procedures and rules that allow two or more applications to talk to each other. An example is a weather app on your smartphone. This app talks to the weather agency's software system and retrieves weather predictions to be displayed on your phone.

The two main parts of this technology are the client and the server. The client is the app sending the request, and the server is the app responding to the request. In the weather example above, your mobile app is the client, and the weather agency's database is the server.

API technologies

APIs employ a variety of technologies for client-server exchange, with the most important ones listed below.

Simple Object Access Protocol (SOAP): The client and server exchange information using XML document format.
Remote Procedure Calls (RPC): The client completes a procedure on the server, and the server sends an output to the client.
Websocket: A protocol for data exchange, providing full-duplex communication.
Webhook: Data exchange is triggered by specific events.
Representational State Transfer (REST): The client sends data requests to the server. The server responds to these requests and outputs data to the client. This is the most flexible and popular type of API.

REST

REST is in fact not a standard, it’s just a loosely defined architecture based on certain principles and technologies (HTTP, JSON, XML etc.) HTTP-based RESTful APIs are defined with the following aspects:

the URI of one or several resources is used as a starting point (also called endpoint)
the resource contains hyperlinks that can be followed to make additional requests
the request will return a representation of a resource and may change the state of the system

The defining feature of the REST API format is statelessness. Statelessness implies that the server does not keep any data from the client between different requests. Each request contains enough information to be executed separately.

Client requests to a server are similar to typing a URL in your browser to open a website. The server's response will typically be an HTML, XML or JSON document.

REST defines a set of functions a client can use to access the server's data. Data is exchanged over HTTP. The main functions include:

GET to fetch a resource
DELETE to remove the source
POST to create a resource
PUT to update a resource

History of RESTful APIs

Before the year 2000, there was no standard approach for designing and using an API. Integrations required using different protocols that were difficult to build and maintain. It all changed in the year 2000 when a group of computer programmers led by Roy Fielding invented REST, a way for computer programs to talk to each other and exchange information.

The programmers designed a set of principles and constraints to enable two or more servers to exchange data anywhere in the world. Fielding identified the need for a low entry barrier and led the team to make REST as easy to use as possible. The result is what’s currently the most popular API standard.

One of the first implementations of the RESTful API came from eBay, a popular online marketplace. The platform's APIs enabled other websites to retrieve data from it in just a few steps. It was easy to use and had extensive documentation to guide developers.

eBay developers program

The adoption increased eBay's visibility across the web, and many other platforms soon followed suit after witnessing eBay's success.

RESTful API Design and Architecture Constraints

An API must align with six core principles to be considered RESTful.

Client-Server Independence: The client and server computer programs must be completely independent. The client only needs to know the server's Uniform Resource Identifier (URI); it can not interact with the server in any other way. Similarly, the server's only job is to pass requested data to the client.
Statelessness: Each request must contain all the necessary information for processing it. Server applications can not store any data about a client request, so each request must have enough information to be executed on its own.
Uniform interface: All API requests for the same server must look the same, regardless of where it comes from. In other words, all clients must talk to the server in a single language, regardless of their architectural backends.
Layered system architecture: The calls and responses must go through different communication layers. Never assume that the client and server apps communicate directly; there can be different intermediaries in the communication loop. Developers must design REST APIs such that neither the client nor the server can tell if the communication occurs directly or via an intermediary.
Cacheability: A cache is an intermediate layer of software that stores data to enable future requests to be executed faster. Requested resources should be cacheable either on the client or server side for faster implementation.
Code on demand (optional): The server usually sends static resources in response to a command. However, responses may contain executable code in certain circumstances. If so, the code should run only on demand.

How REST APIs Work

Rest APIs receive requests for a resource and return all relevant information about the requested resource, translated into a format that the client can interpret. They communicate through HTTP requests to carry out standard database operations like creating, reading, updating and deleting data records, popularly known as CRUD.

For example, you may want to build a program that integrates with Spotify, a popular music streaming app. You can request data about specific audio using Spotify's REST API. It will respond to your request with information like the name of the audio, the date it was published, the streaming count, and how many times it was shared, all packaged in a format your app can understand. Similarly, your app could publish audio on Spotify by communicating with its API.

Spotify for Developers

REST APIs deliver information in various file formats, including plain text, XML, HTML, and JavaScript Object Notation (JSON). JSON is the most popular format because both humans and machines can read it, and it works with all programming languages.

Benefits of REST APIs

Scalability and Flexibility: REST APIs are easy to scale as your app grows because of the client and server separation. It’s also easier to integrate than most other API types.
Expansion: They make expanding your application and adding features easy. For instance, you own a ride-hailing app and must add a map. You don’t need to build your own map solution from scratch when you can just use the APIs of dedicated providers like Mapbox and Google Maps. This saves you a lot of time and stress in expanding your app.
Uniform Interface: Developers agree to adhere to the same standards when building a REST API. Hence, their apps give consistent outputs to clients that request data from them.
File formats: It is compatible with various file formats, and you’re free to choose the one that suits your app. Other API types only send requested information in one or two file formats, unlike REST, which supports many.
Popularity: An outstanding 90% of developers use the RESTful API structure, making it the most popular one globally. This means it's easier for your app to communicate with others if you select this option. Finding tutorials and guides to implement REST API standards is also easier than other standards.

Common REST API Challenges

You’ll likely encounter common challenges when implementing this type of API. They include:

1. Versioning

Versioning refers to making changes to your APIs and ensuring that the changes don't disrupt the function for existing users. You must decide upfront when and how to version your APIs and communicate with the users if need be.

Sometimes, you may need to make a breaking change that’ll affect the backward compatibility of your APIs. It’s essential to communicate with users when making this type of change. However, it isn't essential if it’s a non-breaking change that won’t affect the functionality.

2. Response Times

You must pay attention to your APIs' response times and ensure they respond as fast as possible. When an API is newly launched, it'll have a low volume of data and likely perform well. But, as more people use it and the data volume increases, performance may lag. You’ll need to implement certain features, such as caching, to improve the speed.

3. Security

Hackers frequently exploit weaknesses in APIs to steal data and use it for malicious purposes. An insecure API could cause big losses, so making it as secure as possible is necessary. Encrypt your requests and responses, implement access control, and validate your data, among other practices.

REST API Best Practices

Best practices for implementing REST APIs include:

1. Accept and Respond to Requests with JSON

JSON is the most popular file format for exchanging data via APIs. Your API should accept requests in JSON and respond in the same file format. Otherwise, developers may find it difficult to connect your app with theirs.

2. Extensive Documentation

Documentation is crucial for every API. It is the first thing developers will read when they want to integrate their apps. Your API should have well-organized documentation explaining everything about it. It should be neatly written and compiled such that anyone that reads it can understand what your API is about.

3. Encrypt Requests and Responses

Any request or response from your server should be encrypted to prevent hackers from intercepting it in transit. Use Secure Sockets Layer (SSL)/Transport Layer Security (TLS) protocols to encrypt the information in transit and decrypt it once it gets to the intended recipient. For instance, UniOne’s email API enables you to send encrypted transactional emails and prevent hackers from snooping in on sensitive details.

Conclusion

REST APIs make it easy for developers to build new features for their apps by communicating with other apps. For instance, you can use UniOne’s APIs to send bulk emails with lightning speed.

We’ve explained what REST APIs are, how they work, their benefits, challenges, and the best practices for implementing them. At this point, you should have a basic understanding of this API type and how to proceed with it.

REST API: How It Works, Its History, Benefits, and Common Challenges