What is REST API?

A REST API (Representational State Transfer) is a web architecture principle that allows systems to communicate using HTTP methods and resources (URLs). It’s lightweight, stateless, and widely used for connecting mobile apps, web applications, and cloud services.

For example, when your mobile app fetches user data from a server — it’s making a REST API call.

Core Principles of REST API

Common HTTP Methods in REST API

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REST API Example Structure

GET     /api/products        → Fetch all products  
GET     /api/products/10     → Fetch a specific product  
POST    /api/products        → Add a new product  
PUT     /api/products/10     → Update product details  
DELETE  /api/products/10     → Delete product  

Example: REST API Call using JavaScript Fetch

fetch('https://jsonplaceholder.typicode.com/posts')
  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => console.error('Error fetching data:', error));

POST Example:

fetch('https://jsonplaceholder.typicode.com/posts', {
  method: 'POST',
  headers: {'Content-Type': 'application/json'},
  body: JSON.stringify({
    title: 'Learning REST API',
    body: 'This is a RESTful example',
    userId: 5
  })
})
.then(response => response.json())
.then(data => console.log('Created:', data));

PHP REST API Example

<?php
$apiURL = "https://jsonplaceholder.typicode.com/posts";
$data = array("title" => "New Post", "body" => "Learning REST API", "userId" => 10);

$options = array(
  "http" => array(
    "header"  => "Content-Type: application/json\r\n",
    "method"  => "POST",
    "content" => json_encode($data),
  ),
);

$context = stream_context_create($options);
$result = file_get_contents($apiURL, false, $context);
echo $result;
?>

Node.js REST API Example

const express = require('express');
const app = express();
app.use(express.json());

let users = [{ id: 1, name: "Alice" }];

app.get('/api/users', (req, res) => res.json(users));

app.post('/api/users', (req, res) => {
  const newUser = { id: users.length + 1, name: req.body.name };
  users.push(newUser);
  res.status(201).json(newUser);
});

app.listen(3000, () => console.log('Server running on port 3000'));

Python REST API Example

from flask import Flask, jsonify, request

app = Flask(__name__)
users = [{"id": 1, "name": "Alice"}]

@app.route("/api/users", methods=["GET"])
def get_users():
    return jsonify(users)

@app.route("/api/users", methods=["POST"])
def add_user():
    new_user = request.json
    users.append(new_user)
    return jsonify(new_user), 201

if __name__ == "__main__":
    app.run(debug=True)

HTTP Response Codes Reference Table

REST API Authentication Techniques

Working with JSON in REST APIs

Convert JavaScript object to JSON:

const obj = { name: "Bob", age: 25 };
console.log(JSON.stringify(obj));

Parse JSON response:

let json = '{"status":"success"}';
let data = JSON.parse(json);
console.log(data.status);

REST API CRUD Operations Cheatsheet

REST API Best Practices

✅ Use HTTPS for all API calls
✅ Keep endpoints noun-based (/users, /products)
✅ Use versioning (/api/v1/...)
✅ Handle errors gracefully with clear JSON responses
✅ Document APIs using Swagger or Postman
✅ Test using curl, Postman, or Insomnia

FAQ — REST API Cheatsheet

Q1. What does REST stand for?
REST means Representational State Transfer, a standard way for systems to exchange data over HTTP.

Q2. What’s the difference between REST and SOAP APIs?
REST is lightweight and uses JSON, while SOAP uses XML and more strict messaging protocols.

Q3. How do I test a REST API?
You can use Postman, curl, or built-in browser tools to send and inspect requests.

Q4. What is an endpoint in REST API?
An endpoint is a specific URL where an API can be accessed — e.g., /api/products/1.

Q5. Can REST API return XML instead of JSON?
Yes. Though JSON is standard, you can configure REST APIs to return XML responses if needed.