What is REST API?

Posted by Vinay Vernekar 17th October 2025

Understanding REST API: A Clear, Interview-Friendly Explanation

REST API (Representational State Transfer API) is a widely used architectural style for designing networked applications. It leverages standard HTTP methods to enable communication between clients and servers in a simple, scalable, and stateless way. REST APIs are essential for integrating systems, building web services, and enabling modern mobile and single-page applications.

Key Principles of REST

REST is defined by several core principles that make it suitable for web-scale applications:

  • Statelessness: Each request from client to server must contain all the information needed to understand and process the request. The server does not store client context between requests.
  • Uniform Interface: A consistent, resource-based approach using standard HTTP methods (GET, POST, PUT, PATCH, DELETE) and status codes.
  • Resources and Representations: Resources (e.g., users, accounts, orders) are identified by URIs and can have multiple representations (JSON, XML, etc.).
  • Layered System: Architecture can be composed of layers (caching, load balancing, proxies) which improve scalability and manageability.
  • Cacheability: Responses can be explicitly marked cacheable to improve performance.

Common HTTP Methods and Their CRUD Mapping

REST maps HTTP verbs to CRUD operations:

  • GET — Read (retrieve) a resource
  • POST — Create a new resource
  • PUT — Replace an existing resource
  • PATCH — Partially update a resource
  • DELETE — Remove a resource

Example: Simple REST Request (JSON)

POST /api/accounts HTTP/1.1
Host: api.example.com
Content-Type: application/json

{
"name": "Acme Corporation",
"industry": "Manufacturing"
}

Server response (201 Created):

HTTP/1.1 201 Created
Location: /api/accounts/12345
Content-Type: application/json

{
"id": "12345",
"name": "Acme Corporation",
"industry": "Manufacturing"
}

Why REST API Matters

REST APIs are language-agnostic and simple to consume, making them ideal for microservices, mobile backends, and public web APIs. They promote loose coupling between client and server, allow independent evolution of components, and are supported by extensive tooling and HTTP standards.

Best Practices for Designing REST APIs

  • Use meaningful, pluralized resource names: /api/customers, /api/orders.
  • Return appropriate HTTP status codes (200, 201, 204, 400, 401, 404, 500).
  • Support filtering, pagination, and sorting for list endpoints.
  • Version your API using the URL or headers: /v1/customers or Accept: application/vnd.example.v1+json.
  • Provide clear error responses with codes and messages.

Interview Tip

When asked about REST API in an interview, explain the core REST constraints, map HTTP methods to CRUD operations, and provide a concise example (request/response) to demonstrate practical understanding. Mention differences vs. alternatives like SOAP or GraphQL if prompted.

Keywords: REST API, Representational State Transfer, HTTP methods, stateless, CRUD, JSON, web services, API design.

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