what is a REST API and how does it work

Web Service: What Is a REST API and How Does It Work? 

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Last updated: August 10, 2023

Software integration and application communication wouldn’t be the same without REST APIs. An API (Application Programming Interface) is a set of guidelines that define how devices and applications communicate with each other.

For example, how your eCommerce website interacts with shipping software or how your cloud call center system communicates with your fixed or non-fixed VoiP software is determined by API designs.

Many different types of designs can be used to build APIs. However, when it comes to building API for software integration, the REST design often comes out on top. Adopted by giants like Google, Amazon, and Facebook, REST APIs are praised for their interconnectivity with the world’s most popular web applications, along with their versatility and simplicity.

What Is a REST API?

REST (representational state transfer) refers to a set of specific rules that dictate how web service applications communicate over the internet. Therefore, a RESTful API is an API that follows these rules, providing flexibility, bandwidth, and speed advantages to software integrations and communications.

REST APIs serve as the middleman between your client and your host server, fielding resource requests and delivering responses via HTTP. In a REST design, the client initiates the interaction — for example, accessing a webpage via a URL is a commonly used HTTP request.

How Does a REST API Work?

To understand how RESTful APIs transfer data between clients and applications, it helps to split the operation into two processes.

Client Request

A client is a program or person who accesses the services of the API. For example, your program would be the client if you were integrating with a web application like Instagram or Youtube. Your browser would be the client if you were requesting a URL.

The most common HTTP methods are:

  • GET: To retrieve a resource.
  • POST: To create a new resource.
  • PUT: To edit or update an existing resource.
  • DELETE: To delete a resource.

An HTTP request to Instagram’s API, for instance, might be a GET request for a specific video or post or a POST request to upload a new photo.

Similarly, a call center platform integrating with an auto-attendant application might use the PUT command to update a custom greeting or the DELETE command to remove it.

Server Response

A resource refers to the specific information an API provides to a client. This could be anything from hashtags to profiles, comments, web addresses, tweets, etc. All resources have a unique name called a resource identifier, and they’re all stored on a server.

When a client makes a request using a RESTful API, the server transfers a standardized representation of the resource’s state to the client’s system. This means the server does not send the client the actual resource but a representation of its state – i.e., the state of the resource at a particular timestamp.

Responses are sent back in a lightweight format to aid interpretability. The JSON (JavaScript Object Notation) format is popular because it’s readable by both humans and machines and excels in its strides toward promoting web accessibility. It’s also compatible with many other programming languages.

Some alternative API data formats include XML, YAML, CSV, HTML, and plain text.

REST API Constraints

While REST APIs are appreciated for their simplicity and flexibility, they still have to adhere to six constraints to be considered RESTful. These are the guiding principles of REST API designs.

Client-Server Separation

REST explicitly constrains the communication capabilities of both client and server. The client exclusively makes requests, while the server exclusively responds to these. Therefore, the client initiates every interaction, who knows the URI of the requested resource. The server responds by passing on the requested data without the capability to make independent modifications.

The isolation of client and server allows for ease of manageability. There’s no worry over the components inadvertently modifying each other during independent changes, simplifying optimization and scaling processes.

Uniform Interface

Applications and servers can be written in many different languages. Without an intermediary, any correspondence between a client and server risks being poorly translated. So, for the client and server to communicate effectively while also existing independently, they require a uniform interface.

A uniform interface facilitates the decoupling of client and server by providing a standardized language that’s recognized by both components regardless of their backend infrastructure. Typically, the standardized protocol used by REST APIs is HTTP.


A fundamental principle of REST APIs is that all calls are stateless. This means all client-server interactions are independent tasks — every request sent to the server from the client is a brand new request.

Furthermore, the given request contains all of the information the server requires to perform a response, meaning the server doesn’t need to remember any information about past requests.

Thanks to statelessness, the server doesn’t need to store or retrieve client information to complete requests. This makes the server perform quicker and more reliably, so it can manage an increased number of requests due to the lower risk of memory overload.


Because stateless APIs are designed to increase request overhead by handling a large amount of incoming and outbound calls, REST APIs should prioritize data caching. Caching refers to the storage of data on a client’s device and is used to save server resources and increase bandwidth.

A REST API categorizes the data in their responses as either cacheable or non-cacheable. If the data is cacheable, the API will include the specific length of time the information is cacheable for. Once this time has expired, the client will ping the server for updates.

Layered System

It’s essential to recognize that there are typically multiple servers existing between the client and server endpoints.

The intermediary layers between the client and server exist to construct a hierarchical system that balances operations like traffic distribution and caching. These layers operate independently from each other, increasing their architectural stability and further cementing the decoupling of the client and server endpoints.

Thanks to the isolated nature of each layer, a layered REST API architecture system has considerable security and scalability benefits. Attacks can be contained within proxy or specific layers, mitigating security risks to your full architecture.

Layers can also be added, moved, updated, and removed without adverse effects on the overall system. Not only does this support adaptation in alignment with technological advances, but it gives developers increased agency to experiment and optimize.

For example, a call center or customer service team could experiment with their operational hierarchy, gathering results as they go to reduce their AHT (research ‘what is AHT‘ and why you should reduce it to get a clearer idea of the benefits).

Code on Demand

Unlike the other principles, code on demand is optional in a REST design. It’s a feature that permits an API to send run-on-demand code snippets or applets to a client, extending client functionality.


REST APIs reign supreme as a flexible, scalable, and inclusive way to connect components and integrate applications — but there are still many enterprises who swear by SOAP.

As another application-builder that works over HTTP, SOAP (Simple Object Access Protocol) and REST are consistently compared. Let’s take a quick look at what distinguishes REST from SOAP to gain some insight into the advantages and disadvantages of each.

SSOAP Is a Protocol, REST Is a Set of Guidelines

SOAP is a prescribed XML-based messaging protocol with strict standards and syntax. REST is a set of design principles that dictate specific guidelines that developers need to follow but, in many areas, grants copious flexibility.

REST Uses Lightweight Formats

Formats like JSON and HTML are optimized for the internet, whereas XML is bulky and slow. This provides REST with considerable performance advantages, particularly in IoT and mobile app development.

SOAP Is More Complex

SOAP is heavily reliant on XML and schemas, with some programming languages even requiring you to manually build requests. It’s defined by a rigid, logistical structure and is notoriously intolerant of errors. On the other hand, REST has a much smaller learning curve and utilizes standards that are much easier to use.

REST Is More Supportive of Cloud-Native Environments

This isn’t to say SOAP is unsuitable for cloud environments. In fact, if you were developing a mobile banking solution, SOAP’s advanced security provisions might make it preferable. However, REST has the upper hand when it comes to supporting cloud-based automation, communication, and data transfer, largely due to enhanced architectural flexibility and customization advantages.

Examples of REST APIs

APIs power the modern web, so there are thousands of examples of REST APIs throughout the world. For example, Salesforce offers numerous REST APIs that enable third-party developers to integrate its features and extend the platform. The Paypal REST API or Notion API are other popular examples of REST APIs.

Also, it should be noted that some APIs are more RESTful than others. More often than not, “REST” APIs don’t technically adhere to every constraint of Roy Fielding’s definition of REST, since most don’t adopt Hypermedia as the Engine of Application State (HATEOAS).

Of course, REST is not the only API style in the market. SOAP, gRPC, webhooks, and GraphQL are other design styles for APIs. And in recent years, GraphQL has especially been garnering interest due to its easier data retrieval mechanics and usability.

Should You Use REST APIs?

The simple answer — without a doubt.

For startups and small businesses in the tech industry, deploying RESTful APIs offers you the opportunity to interface with global enterprises. Just as you register names for your ai domains or implement a thought leadership strategy to establish credibility in the field, integrating your programs with popular applications cements your businesses as credible and reliable.

REST is clearly an industry standard for web API deployment. While there are certainly other options out there — GraphQL, for example, is a query language that’s growing in popularity — REST boasts an excess of tools, resources, and frameworks to maximize ease of use and versatility.

Isn’t it time you made the most of it?