Ace Your Next REST API Interview: 13 Essential Questions to Know

In the ever-evolving world of software development, REST (Representational State Transfer) APIs have become an integral part of modern web applications and services. As a developer, being well-versed in REST APIs can give you a competitive edge in the job market. In this article, we’ll explore 13 essential REST API interview questions and provide clear, concise explanations to help you excel in your next technical interview.

What is REST?

REST is an architectural style that defines a set of constraints and principles for building web services. It is designed to enable communication between clients and servers over the internet, allowing them to exchange data and perform operations on resources.

What is a REST API?

A REST API, or RESTful API, is a web service that adheres to the principles and constraints of the REST architectural style. It provides a standardized way for clients (such as web browsers, mobile apps, or other services) to interact with resources on a server using a predefined set of operations, typically implemented using HTTP methods like GET, POST, PUT, and DELETE.

Describe the 5 Constraints of the REST Architectural Style, and Their Benefits

The five key constraints of the REST architectural style are:

  1. Client-Server Architecture: Separates the concerns of the client and server components, allowing them to evolve independently and improving scalability.

  2. Stateless: The server does not store any client session data, reducing server complexity and improving reliability.

  3. Cacheable: Responses from the server can be cached by clients or intermediaries, improving performance and scalability.

  4. Layered System: Allows the introduction of intermediaries (e.g., load balancers, proxies) between the client and server, improving system scalability and security.

  5. Uniform Interface: Defines a standard way for clients to interact with resources, simplifying the overall system architecture.

The benefits of these constraints include improved scalability, reliability, performance, and maintainability of web services.

What is the Optional Architectural Constraint of REST?

The optional architectural constraint of REST is Code on Demand. This constraint allows the server to send executable code (e.g., scripts, applets) to the client upon request, extending the client’s functionality dynamically.

Explain the Constraints of a Uniform Interface

The uniform interface constraint is a key principle of the REST architectural style, and it consists of four sub-constraints:

  1. Resource Identification: Resources are identified using Uniform Resource Identifiers (URIs).

  2. Resource Manipulation through Representations: Clients manipulate resources by exchanging representations (e.g., JSON, XML) of those resources with the server.

  3. Self-Descriptive Messages: Each request and response message includes enough information for the recipient to understand and process it without additional context.

  4. Hypermedia as the Engine of Application State (HATEOAS): Clients should be able to discover and navigate through the available resources and actions using hypermedia links provided in the responses.

What is CRUD?

CRUD is an acronym that stands for Create, Read, Update, and Delete. It represents the four basic operations that can be performed on persistent data or resources in a system. These operations correspond to the HTTP methods used in RESTful APIs:

  • Create: Implemented using the HTTP POST method to create a new resource.
  • Read: Implemented using the HTTP GET method to retrieve a representation of a resource.
  • Update: Implemented using the HTTP PUT or PATCH methods to update an existing resource.
  • Delete: Implemented using the HTTP DELETE method to remove a resource.

Explain the HTTP Request Methods Supported by REST, and When They Are Used

REST APIs typically support the following HTTP request methods:

  • GET: Retrieves a representation of a resource. It is a safe and idempotent operation.
  • POST: Creates a new resource on the server. It is not idempotent.
  • PUT: Updates or replaces an existing resource on the server. It is idempotent.
  • PATCH: Partially updates an existing resource on the server.
  • DELETE: Removes a resource from the server. It is idempotent.
  • HEAD: Retrieves the metadata (headers) of a resource without its body.
  • OPTIONS: Returns the HTTP methods that the server supports for a specific resource.

What’s the Difference Between PUT and POST Methods?

The main differences between the PUT and POST methods are:

  • PUT is idempotent, meaning that multiple identical requests will have the same effect as a single request. POST, on the other hand, is not idempotent.
  • PUT requests are typically used to update or replace an existing resource, while POST requests are used to create a new resource.
  • Responses to PUT requests are generally not cacheable, while responses to POST requests can be cacheable.

Explain What Statelessness Means in REST

Statelessness is one of the key constraints of the REST architectural style. It means that the server does not store any client session data or state information between requests. Each request from the client must contain all the necessary information for the server to process it, and the server should not rely on any stored context or session data from previous requests.

The benefits of statelessness include improved scalability, reliability, and simplicity, as the server does not need to manage complex session states or handle resource locking issues.

What Are the Advantages and Disadvantages of a REST API?

Advantages of REST APIs:

  • Scalability: The stateless nature and separation of concerns make REST APIs highly scalable.
  • Flexibility: REST APIs can support various data formats (JSON, XML, etc.) and can be consumed by different clients.
  • Cacheability: Responses can be cached, improving performance and reducing server load.
  • Simplicity: REST APIs use standard HTTP methods and URIs, making them easy to understand and implement.

Disadvantages of REST APIs:

  • Lack of Built-in Security: REST APIs do not provide built-in security mechanisms, and developers must implement appropriate security measures.
  • Over-fetching and Under-fetching: Clients may receive more or less data than they need, leading to inefficiencies.
  • Statelessness: Some applications may require maintaining state information, which can be challenging with stateless REST APIs.

What’s the Difference Between AJAX and REST?

AJAX (Asynchronous JavaScript and XML) is a technique for building web applications that can send and retrieve data asynchronously from the server without reloading the entire page. While AJAX can be used to interact with RESTful APIs, it is not an architectural style itself.

REST, on the other hand, is an architectural style that defines principles and constraints for building web services. A RESTful API can be consumed by various clients, including AJAX-based applications, but it is not inherently implemented using AJAX.

What’s the Difference Between SOAP and REST?

SOAP (Simple Object Access Protocol) and REST are two different approaches to building web services:

  • SOAP is a protocol that defines a strict set of rules and standards for communication between applications, typically using XML for data exchange. It is more complex and heavyweight than REST.
  • REST is an architectural style that relies on standard HTTP methods and URIs for communication and can use various data formats (JSON, XML, etc.). It is generally considered more lightweight and flexible than SOAP.

While SOAP provides built-in security and transaction support, REST APIs rely on the underlying protocols (e.g., HTTPS) for security and do not have built-in transaction management.

Explain HTTP Response Status Codes

HTTP response status codes are standardized codes that indicate the result of a client’s request to a server. Some common HTTP status codes include:

  • 200 OK: The request was successful.
  • 201 Created: A new resource was created successfully.
  • 204 No Content: The request was successful, but there is no content to return.
  • 400 Bad Request: The server could not understand the request due to invalid syntax or input.
  • 401 Unauthorized: Authentication is required to access the requested resource.
  • 403 Forbidden: The client does not have permission to access the requested resource.
  • 404 Not Found: The requested resource could not be found on the server.
  • 500 Internal Server Error: An unexpected error occurred on the server.

Understanding and correctly handling these status codes is crucial for building robust and reliable REST APIs.

By understanding and practicing these 13 essential REST API interview questions, you’ll be well-prepared to demonstrate your knowledge and expertise in technical interviews. Remember, staying up-to-date with the latest trends and best practices in web development, including REST APIs, can give you a significant advantage in your career journey.

REST API Interview Questions (Beginner Level)


What is the basic knowledge of RESTful API?

A RESTful API is an architectural style for an application program interface (API) that uses HTTP requests to access and use data. That data can be used to GET, PUT, POST and DELETE data types, which refers to the reading, updating, creating and deleting of operations concerning resources.

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