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13 December 2023

14 Min. Read

API Testing

What is a REST API? Everything You Need to Know

What is a REST API? Everything You Need to Know

Key Highlights

In this blog, we cover following key highlights:

  1. Learn about what is REST API and how it was invented?

  2. Know the difference between REST and SOAP APIs

  3. Get to know the anatomy of any request with REST API examples

  4. Lastly, learn about the intricacies involved with using REST APIs

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Is a significant part of your daily work routine spent sending API requests and examining the responses, or maybe the other way around? Well, guess what? REST API is like your trusty work buddy.

But what exactly is a REST API, and how does it make your data-fetching tasks better? This article is here to break down the concept of APIs, provide REST APIs examples, and give you all the details you need to use them effectively.

What is an API?

First things first, let's begin from the basics to ensure a solid foundation. What exactly is an API? If you're already well-acquainted with this, feel free to skip this section and jump to the part that addresses your current needs the most.

Simply put, APIs are the backbone of today’s software.

Let’s take the library analogy to understand the meaning of APIs:

Imagine an API as a librarian. You go to a librarian and ask for a book on a specific topic. The librarian understands your request and fetches the book from the shelves. Here, you don’t need to know where the book is or how the library is organized. The API (librarian) abstracts the complexity and presents you with a simple interface - asking for information and receiving it.

API Diagram

Imagine you're using an app like "Agoda" to find a hotel room. Behind the scenes, a bunch of API requests are at play, darting around to compile the list of available rooms. It's not just about clicking buttons; APIs do the behind-the-scenes work. They process your request, gather responses, and that's how the whole frontend and backend system collaborates.

So an API could be anything in any form. The only thing that it has to be is that it has to be a way to communicate with a software component.

Types of APIs

Each type of API serves a unique purpose and caters to different needs, just as different vehicles are designed for specific journeys.

  1. Open APIs (Public Transport): Open APIs are like public buses or trains. They are available to everyone, providing services that are accessible to any developer or user with minimal restrictions. Just as public transport follows a fixed route and schedule, open APIs have well-defined standards and protocols, making them predictable and easy to use for integrating various applications and services.

  2. Internal APIs (Company Shuttle Service): These APIs are like the shuttle services provided within a large corporate campus. They are not open to the public but are used internally to connect different departments or systems within an organization. Like a shuttle that efficiently moves employees between buildings, internal APIs enable smooth communication and data exchange between various internal software and applications.

  3. Partner APIs (Car Pooling Services): Partner APIs are akin to carpooling services where access is granted to a select group of people outside the organization, usually business partners. They require specific rights or licenses, much like how a carpool requires a shared destination or agreement among its members. These APIs ensure secure and controlled data sharing, fostering collaboration between businesses.

  4. Composite APIs (Cargo Trains): Just as a cargo train carries multiple containers and combines different goods for efficient transportation, composite APIs bundle several service calls into a single call. This reduces the client-server interaction and improves the performance of listeners in web interfaces. They are particularly useful in microservices architectures, where multiple services need to interact to perform a single task.

  5. REST APIs (Electric Cars): REST (Representational State Transfer) APIs are the electric cars of the API world. They are modern, efficient, and use HTTP requests to GET, PUT, POST, and DELETE data. Known for their simplicity and statelessness, they are easy to integrate and are widely used in web services and applications.

  6. SOAP APIs (Trains): SOAP (Simple Object Access Protocol) APIs are like trains. They are an older form of API, highly standardized, and follow a strict protocol. SOAP APIs are known for their security, transactional reliability, and predefined standards, making them suitable for enterprise-level and financial applications where security and robustness are paramount.

  7. GraphQL APIs (Personalized Taxi Service): GraphQL APIs are like having a personalized taxi service. They allow clients to request exactly what they need, nothing more and nothing less. This flexibility and efficiency in fetching data make GraphQL APIs a favorite for complex systems with numerous and varied data types.

What is a REST API?

Coming back to the topic of this piece, let’s dive deep and discuss all about REST APIs.

A REST API or REST web service is an API that follows that follows the rules of REST specification. A web service is defined by these rules:

  • How software components will talk?

  • What kind of messages they’ll send to each other?

  • How requests and responses will be handled?

A REST API, standing for Representational State Transfer API, is a set of architectural principles for designing networked applications. It leverages standard HTTP protocols and is used to build web services that are lightweight, maintainable, and scalable.

You make a call from a client to a server, and you get the data back over the HTTP protocol.

Architectural Style

REST is an architectural style, not a standard or protocol. It was introduced by Roy Fielding in his 2001 doctoral dissertation. A RESTful API adheres to a set of constraints which, when followed, lead to a system that is performant, scalable, simple, modifiable, visible, portable, and reliable.

REST itself is an underlying architecture of the web.

Principles of REST

REST APIs are built around resources, which are any kind of objects, data, or services that can be accessed by the client. Each resource has a unique URI (Uniform Resource Identifier).

An API qualifies as a REST API if it follows these principles:

  1. Client-Server Architecture: The client application and the server application must be able to operate independently of each other. This separation allows for components to evolve independently, enhancing scalability and flexibility.

  2. Statelessness: Each request from the client to the server must contain all the information needed to understand and process the request. The server should not store any session state, making the API more scalable and robust.

  3. Cacheability: Responses should be defined as cacheable or non-cacheable. If a response is cacheable, the client cache is given the right to reuse that response data for later, equivalent requests.

  4. Layered System: A client cannot ordinarily tell whether it is connected directly to the server or to an intermediary along the way. Intermediary servers can improve system scalability by enabling load balancing and shared caches.

  5. Uniform Interface: This principle simplifies the architecture, as all interactions are done in a standardized way. It includes resource identification in requests, resource manipulation through representations, self-descriptive messages, and hypermedia as the engine of application state (HATEOAS).

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REST API Example

It is always better to understand things with the help of examples, so let’s do the same with this and dive deeper into this REST API example.

👉Imagine a service that manages a digital library. This service provides a REST API to interact with its database of books. A client application wants to retrieve information about a specific book with the ID 123.

Anatomy of the Request

1. Endpoint URL

The endpoint is the URL where your API can be accessed by a client application. It represents the address of the resource on the server which the client wants to interact with.



  • Base URL: - The root address of the API.

  • Path: /books/123 - Specifies the path to the resource. In this case, books is the collection, and 123 is the identifier for a specific book.

2. HTTP Method

This determines the action to be performed on the resource. It aligns with the CRUD (Create, Read, Update, Delete) operations.

Example: GET

  • Purpose: In this case, GET is used to retrieve the book details from the server.

3. Headers

Headers provide metadata about the request. They can include information about the format of the data, authentication credentials, etc.


  • Content-Type: application/json - Indicates that the request body format is JSON.

  • Authorization: Bearer your-access-token - Authentication information, if required.

4. Request Body

This is the data sent by the client to the API server. It's essential for methods like POST and PUT.

Example: Not applicable for GET requests, as there is no need to send additional data.

  • Purpose: For other methods, it might include details of the resource to be created or updated.

5. Query Parameters

These are optional key-value pairs that appear at the end of the URL. They are used to filter, sort, or control the behavior of the API request.


  • Purpose: In this example, the query parameters request the book in PDF format and specify that the latest version is needed.

6. Response


  • Status Code: Indicates the result of the request. E.g., 200 OK for success, 404 Not Found for an invalid ID, etc.

  • Response Body: The data returned by the server. For a GET request, this would be the details of the book in JSON or XML format.

  • Response Headers: Contains metadata sent by the server, like content type or server information.

Client-Server Interaction in the REST API World

Let's put everything together in a detailed request example:

Endpoint URL:

HTTP Method: GET


  • Accept: application/json (tells the server that the client expects JSON)

  • Authorization: Bearer your-access-token (if authentication is required)

Request Body: None (as it's a GET request)

Query Parameters: None (assuming we're retrieving the book without filters)

  • The client sends this request to the server. The server processes the request, interacts with the database to retrieve the book's details, and sends back a response. The response might look like this:

Status Code: 200 OK

Response Body:

    "id": 123,
    "title": "Learning REST APIs",
    "author": "Jane Doe",
    "year": 2021

Response Headers:

  • Content-Type: application/json; charset=utf-8

The HTTP Methods and REST World

In the realm of RESTful web services, HTTP methods are akin to the verbs of a language, defining the action to be performed on a resource. Understanding these methods is crucial for leveraging the full potential of REST APIs.

Let's delve into each of these methods, their purpose, and how they are used in the context of REST.

1. GET: Retrieve data from a server at the specified resource

  • Safe and idempotent: Does not alter the state of the resource.

  • Used for reading data.

  • Example:

  .then(response => response.json())
  .then(data => console.log(data));

2. POST: Send data to the server to create a new resource

  • Non-idempotent: Multiple identical requests may create multiple resources.

  • Commonly used for submitting form data.

  • Example:

fetch('<>', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
  body: JSON.stringify({ name: 'New Item', price: 20 })
.then(response => response.json())
.then(data => console.log(data));

3. PUT: Update a specific resource (or create it if it does not exist)

  • Idempotent: Repeated requests produce the same result.

  • Replaces the entire resource.

  • Example:

fetch('<>', {
  method: 'PUT',
  headers: {
    'Content-Type': 'application/json',
  body: JSON.stringify({ name: 'Updated Item', price: 30 })
.then(response => response.json())
.then(data => console.log(data));

4. DELETE: Remove the specified resource

  • Idempotent: The resource is removed only once, no matter how many times the request is repeated.

  • Used for deleting resources.

  • Example:

fetch('<>', {
  method: 'DELETE'
.then(() => console.log('Item deleted'));

5. PATCH: Partially update a resource

  • Non-idempotent: Repeated requests may have different effects.

  • Only changes specified parts of the resource.

  • Example:

fetch('<>', {
  method: 'PATCH',
  headers: {
    'Content-Type': 'application/json',
  body: JSON.stringify({ price: 25 })
.then(response => response.json())
.then(data => console.log(data));

RESTful Design Considerations

When designing a RESTful service, it's important to adhere to the intended use of each HTTP method:

  • Use GET for retrieving data.

  • Use POST for creating new resources and actions that do not fit into the other methods.

  • Use PUT and PATCH for updates, with PUT for full updates and PATCH for partial updates.

  • Use DELETE for removing resources.

Proper use of these methods ensures clarity and consistency in your API, making it more intuitive and easier to use for developers. This approach adheres to the REST architectural style, promoting stateless communication and standardized interactions between clients and servers.

How REST is different from SOAP?

REST (Representational State Transfer) and SOAP (Simple Object Access Protocol) are two different approaches to web service communication, each with its unique characteristics and use cases. Understanding their differences is key to choosing the right protocol for a specific application. Let's explore how REST and SOAP differ in various aspects:

1. Design Philosophy and Style

  • REST:

    • REST is an architectural style rather than a protocol.

    • It is based on the principles of statelessness, cacheability, and a uniform interface, leveraging standard HTTP methods like GET, POST, PUT, and DELETE.

    • REST is resource-oriented; each URL represents a resource, typically an object or a service.

  • SOAP:

    • SOAP is a protocol defined by a standard set of rules and has a stricter set of messaging patterns.

    • It focuses on actions and operations rather than resources.

    • SOAP messages are typically wrapped in an XML envelope, which can contain headers and body content.

2. Data Format

  • REST:

    • RESTful services can use various data formats, including JSON, XML, HTML, and plain text, but JSON is the most popular due to its lightweight nature and ease of use with web technologies.

  • SOAP:

    • SOAP exclusively uses XML for sending messages. This can lead to larger message sizes and more parsing overhead compared to JSON.

3. Statefulness

  • REST:

    • REST is stateless; each request from a client to a server must contain all the information needed to understand and complete the request.

    • Statelessness helps in scaling the application as the server does not need to maintain, update, or communicate the session state.

  • SOAP:

    • SOAP can be either stateful or stateless, though it often leans towards stateful operations. This means that SOAP can maintain state across multiple messages or sessions.

For the complete list of differences between REST and SOAP APIs, click here to download it.

How does REST APIs work?

When a RESTful API is called, the server transfers a representation of the state of the requested resource to the requesting client. This information, or representation, is delivered in one of several formats via HTTP: JSON (JavaScript Object Notation), HTML, XLT, Python, PHP, or plain text.

JSON is the most popular due to its simplicity and how well it integrates with most programming languages.

The client application can then manipulate this resource (through editing, deleting, or adding information) and request the server to store this new version. The interaction is stateless, meaning that each request from the client contains all the information the server needs to fulfill that request.

👉It uses HTTP method suitably(GET for getting data, PUT/ PATCH for updating, POST for putting data, DELETE for deleting)

👉Scoping information (and other data) goes in the parameter part of the URL.

👉It uses common data formats like JSON and XML (most commonly used is JSON)

👉Communication is stateless

REST API Advantages

As we delve into the world of web services and application integration, REST APIs have emerged as a powerful tool. Here are some key benefits:

1. Simplicity and Flexibility

  • Intuitive Design: REST APIs use standard HTTP methods, making them straightforward to understand and implement. This simplicity accelerates development processes.

  • Flexibility in Data Formats: Unlike SOAP which is bound to XML, REST APIs can handle multiple formats like JSON, XML, or even plain text. JSON, in particular, is favored for its lightweight nature and compatibility with modern web applications.

2. Statelessness

  • No Session Overhead: Each request in REST is independent and contains all necessary information, ensuring that the server does not need to maintain session state. This statelessness simplifies server design and improves scalability.

  • Enhanced Scalability and Performance: The stateless nature of REST facilitates easier scaling of applications. It allows servers to quickly free up resources, enhancing performance under load.

3. Cacheability

  • Reduced Server Load: REST APIs can explicitly mark some responses as cacheable, reducing the need for subsequent requests to hit the server. This caching mechanism can significantly improve the efficiency and performance of applications.

  • Improved Client-Side Experience: Effective use of caches leads to quicker response times, directly impacting user experience positively.

4. Uniform Interface

  • Consistent and Standardized: REST APIs provide a uniform interface, making interactions predictable and standardized. This uniformity enables developers to create a more modular and decoupled architecture.

  • Ease of Documentation and Understanding: A standardized interface aids in creating clearer, more concise documentation, which is beneficial for onboarding new team members or integrating external systems.

5. Layered System

  • Enhanced Security: The layered architecture of REST allows for additional security layers (like proxies and gateways) to be introduced without impacting the client or the resource directly.

  • Load Balancing and Scalability: REST's layered system facilitates load balancing and the deployment of APIs across multiple servers, enhancing scalability and reliability.

6. Community and Tooling Support

  • Widespread Adoption: REST's popularity means a large community of developers and an abundance of resources for learning and troubleshooting.

  • Robust Tooling: A plethora of tools and libraries are available for testing, designing, and developing REST APIs, further easing the development process.

7. Platform and Language Independence

  • Cross-Platform Compatibility: REST APIs can be consumed by any client that understands HTTP, making them platform-independent.

  • Language Agnostic: They can be written in any programming language, offering flexibility in choosing technology stacks according to project needs.

8. Easy Integration with Web Services

  • Web-Friendly Nature: REST APIs are designed to work seamlessly in a web environment, taking advantage of HTTP capabilities.

  • Compatibility with Microservices: The RESTful approach aligns well with the microservices architecture, promoting maintainable and scalable system design.

REST API Challenges

Addressing REST API challenges is crucial for engineering leads and developers who are pivotal in navigating the complexities of API development and integration. Despite the numerous advantages of REST APIs, there are several challenges that teams often encounter. Recognizing and preparing for these challenges is key to ensuring successful implementation and maintenance of RESTful services.

  • REST APIs are stateless; they do not retain information between requests. This can be a hurdle in scenarios where session information is essential.

  • REST APIs typically define endpoints for specific resources. This can lead to overfetching (retrieving more data than needed) or underfetching (needing to make additional requests for more data).

  • Evolving a REST API without breaking existing clients is a common challenge. Proper versioning strategy is essential.

  • Managing the load on the server by implementing rate limiting and throttling is essential but tricky. Poorly implemented throttling can lead to denied services for legitimate users or allow malicious users to consume too many resources.

  • Developing a consistent strategy for error handling and providing meaningful error messages is essential for diagnosing issues.

  • Effectively handling nested resources and relationships between different data entities in a RESTful way can be complex. This may result in intricate URL structures and increased complexity in request handling.

Why Choose HyperTest for Testing Your Restful APIs?

REST APIs play a crucial role in modern web development, enabling seamless interaction between different software applications. Ensuring they are always secured and working efficiently, testing them thoroughly becomes a key factor.

HyperTest is a cutting-edge testing tool designed for RESTful APIs. It offers a no-code solution to automate integration testing for services, apps, or APIs, supporting REST, GraphQL, SOAP, and gRPC.

👉Generating integration tests from network traffic

👉Detecting regressions early in the development cycle

👉Load testing to track API performance, and

👉Integration with CI/CD pipelines for testing every commit.

Its innovative record-and-replay approach saves significant time in regression testing, ensuring high-quality application performance and eliminating rollbacks or hotfixes in production.

To learn more about how it helped a FinTech company serving more than half a million users, please visit HyperTest.

Frequently Asked Questions (FAQs)

1. What are the main benefits of using REST APIs?

REST APIs offer simplicity, scalability, and widespread compatibility. They enable efficient data exchange, stateless communication, and support various client types, fostering interoperability in web services.

2. How is REST API useful?

REST APIs facilitate seamless communication between software systems. They enhance scalability, simplify integration, and promote a stateless architecture, enabling efficient data exchange over HTTP. With a straightforward design, REST APIs are widely adopted, fostering interoperability and providing a robust foundation for building diverse and interconnected applications.

3. What is the difference between API and REST API?

An API is a broader term, referring to a set of rules for communication between software components. REST API (Representational State Transfer) is a specific type of API that uses standard HTTP methods for data exchange, emphasizing simplicity, statelessness, and scalability in web services.
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