What is a REST API?

Imagine that you’re a software developer. You have an app to build, launch, and get to market in a relatively short amount of time. Your website customers won’t settle for less than the best user experience imaginable. And, frustratingly, you’re playing web development catch-up with the new kids on the block — a trendy start-up called something like Zip or Zap or Zip-zap-zonk.

You think the name is really dumb, but you have to admit that their app is fantastic. You’re a bit jealous.

However, you’ve never been one to give up. And although your job is on the line and your web services dev team is small, your customers’ heads are ripe for turning and in terms of REST API design, you have a trick or two up your sleeve.

You know the advantages of REST APIs (application programming interfaces). You can expertly use them to add the functionality to supercharge your company’s app with the latest features and drive best-in-class customer experiences. The world of software integration is your oyster. What will you come up with?

The modern app experience

The beauty of REST APIs (also known as RESTful APIs; REST stands for representational state transfer), is their simple yet transformative technology. REST APIs have quickly become the backbone and building blocks of modern app and website experiences. 

But before considering the aspects of REST APIs, let’s start by knowing something about plain-old standard APIs.

What is an API?

An API is a software intermediary that lets software programs connect and communicate with each other. It’s important technology because in this digital world where everything is connected 24×7, software integration is crucial. Apps and programs must be able to expertly and efficiently make contact and chat in order to provide people with access to all sorts of data and functionality. An API is the special sauce that lets it all happen. 

There are different types of APIs. Or it might be more accurate to say that there are different guidelines or architectural styles that govern how two software programs communicate using an API.

What is a REST API?

REST is a collection of rules that developers follow when creating APIs; a set of principles governing how different programs communicate. So a REST API is simply an API that applies these principles.

When a client, a program making a request to connect with an API, requests a resource (information that can be communicated and shared using an API), the existing state of the resource is transferred back by the server in a standardized representation.

One of the rules of REST is that you should get a piece of data (a resource) when you link to a particular URL. REST APIs allow a request for a resource to go from the client to the server, and then for relevant information to be sent back as a response.

A request consists of an endpoint (the URL you request for), a method, which defines the type of request sent to the server; headers, which represent the metadata; and data. 

REST methods

You’ve probably heard of the main methods associated with REST APIs:

GET: The server finds the requested data and sends it to you when the GET request is used.

PUT: Using PUT requests means the server updates a database entry.

POST: With the POST method, the server creates a database entry.

DELETE: As the name implies, the server deletes a database entry with a DELETE request.

REST API examples

Did you know that Gmail, Twitter, and Instagram are all well known examples of REST APIs? Yep, this technology is pretty pervasive. 

What does the functionality of a REST API look like? One example of a REST API in action is music-streaming service Spotify, whose API allows app developers to bring information about songs, albums, artists, and playlists into their own app experiences. For instance, think of a fitness-tracking app that lets people access Spotify and get pumped by their favorite workout tunes. APIs are the connectors making this type of multifaceted functionality possible and driving apps’ success.

The best of the REST

While there are other API architectures out there, including SOAP (Simple Object Access Protocol) and XML-RPC (remote procedure call), REST stands out. The consensus is that REST architecture APIs are close to becoming the industry standard for web-based software development.

What makes this process so special in software-development circles? What are the advantages of REST APIs over other architectures?

REST APIs stand out due to their simplicity. They allow any two web applications to connect, communicate, and share data. With REST, you can integrate your app or software program with any other software app or program, regardless of whether the host organization is a multinational company, a government agency, or a small start-up.

Here are the main benefits of using REST APIs:

  • Flexibility: REST APIs can handle a multitude of different types of client requests and data formats
  • Simplicity: All the client needs to make a request for a resource is the server’s URL
  • Scalability: As your app grows, REST APIs ensure that adding more resources or a variety of requests won’t affect performance

With this freedom, app developers can piece together the building blocks of the modern app experience. It’s quick and easy to create market-leading functionality to enhance and complement your app.

Now you know why a REST API is a must-have for certain features. You should also know that some guidelines must be followed.

The rules according to REST 

What are the requirements for developers’ using REST APIs? Here are the generally accepted software architectural constraints developers must follow in order to ensure successful REST API functionality:

Separation of client and server

The client and server can communicate in only one format: with a request from a client to a server. That client-server setup means limited scope. Requests can’t be made by servers and responses can’t be sent by clients. Why is this way of operating helpful? It keeps servers and clients operating completely independently, which means that their actions can’t adversely impact each other.

Use of a uniform interface (UI)

The formatting language used for clients and REST APIs to communicate must be the same, otherwise miscommunication could be a problem. In most cases, RESTful web services use HTTP (Hypertext Transfer Protocol) as the language spoken between client and server.


A stateless transaction is an interaction-independent one, and REST is intended to be stateless. The server interprets each request as brand new, even if the same exact request has already been made. Every communication between the client and server must include all the necessary information. The advantages? Lower amounts of server memory are used and interactions are scalable.

Because they’re stateless, REST APIs are often used for cloud applications. In the event of a failure, the components can be redeployed and expanded to handle changes in workload. Some other relevant applications for REST APIs: cloud services, an iOS app, and client-side web projects.

A layered system

In a seemingly simple interaction between a client and a server, the reality is that additional servers (“layers”) between them are usually part of the communication process. The extra layers distribute traffic and add security, among other helpful functions.

Cacheable responses

Server resources can be conserved and page-loading time can be shortened when caching is used — keeping information stored on the client side. REST has an advantage here because it is more amenable to caching than SOAP. 

Code on demand (optional)

The server can give the REST client more functionality by sending code that can be executed by the client. One example would be a JavaScript-powered web app consuming a REST API; the server could send JavaScript code to the browser. However, a key disadvantage is that code on demand (COD) reduces visibility. 

We REST our case…

Well, that sums it up — hope you’ve learned everything you wanted to know from this little REST API tutorial.

Now that you know all about REST, you’re undoubtedly thinking about how you might be able to use it to create world-class web-page search experiences for your customers. Algolia provides enterprise-grade APIs for both fundamentals of the modern-day app, search and recommendations; our REST APIs can help you realize your goals pronto. 

Our Search REST API, the core of our offering, is surrounded by an ecosystem of libraries, tools, and a dashboard. You can use our official API clients and libraries, which are all open source, and the code is right there on GitHub. 

To see about how you can start zip-zapping your trendy competition, contact our team. In no time, you’ll be driving hyperpersonalized user experiences that could conceivably be as awesome as Amazon’s and as spot on as Spotify’s.

About the authorCatherine Dee

Catherine Dee

Search and Discovery writer

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