What Is a REST API? A Clear Guide for Beginners
Understand REST APIs — what they are, how HTTP methods work, and how to interact with APIs.
What Is an API?
API (Application Programming Interface) is a set of rules for how software components communicate with each other. It defines what requests you can make, what format they should be in, and what responses you will receive.
When you use a weather app on your phone, the app calls a weather API that provides current weather data. When you pay via Razorpay, your website calls Razorpay's payment API. APIs are how different software systems exchange data.
REST: The Most Common API Style
REST (Representational State Transfer) is an architectural style for building APIs over HTTP. REST APIs are:
Stateless: Each request contains all information needed. Server does not store session state.
Resource-based: Everything is a "resource" identified by a URL.
HTTP-based: Uses standard HTTP methods.
HTTP Methods in REST APIs
GET: Retrieve data. GET /users/123 returns user with ID 123. Does not change data.
POST: Create new data. POST /users creates a new user with data in the request body.
PUT: Replace data. PUT /users/123 replaces user 123 with new data.
PATCH: Partially update data. PATCH /users/123 updates only specified fields.
DELETE: Remove data. DELETE /users/123 removes user 123.
HTTP Status Codes
200 OK: Request succeeded.
201 Created: Resource created (POST response).
400 Bad Request: Invalid request (missing required field, invalid format).
401 Unauthorized: Authentication required.
403 Forbidden: Authenticated but not permitted.
404 Not Found: Resource does not exist.
429 Too Many Requests: Rate limit exceeded.
500 Internal Server Error: Server-side problem.
JSON: The Universal API Format
REST APIs almost universally use JSON for request and response bodies. Request example:
POST /api/users
Content-Type: application/json
{"name": "Ravi Kumar", "email": "ravi@example.com"}
Response:
{"id": 12345, "name": "Ravi Kumar", "email": "ravi@example.com", "created_at": "2026-01-15"}
Testing APIs
Postman: The most popular API testing tool. GUI-based, excellent for exploration.
cURL: Command-line HTTP client. Available on all operating systems.
Insomnia: Alternative to Postman, clean interface.
Lazyblink JSON Formatter: Format API responses for easy reading.
Frequently asked questions
What is the difference between GET and POST in an API?
GET retrieves data without changing anything on the server. POST sends data to create something new. GET parameters go in the URL; POST data goes in the request body.
What does HTTP 404 mean?
404 Not Found means the requested resource (URL) does not exist on the server. Either the URL is wrong, the resource was deleted, or it never existed.
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