REST API Introduction

beginner
10 min

REST API Introduction

Welcome to the REST APIs course! In this first lesson, you will learn what an API is, what makes an API "RESTful", and why REST APIs power almost every app you use every day.

What is an API?

API stands for Application Programming Interface. It is a set of rules that lets one piece of software talk to another. Think of it like a waiter in a restaurant: you (the client) tell the waiter (the API) what you want, the waiter takes your order to the kitchen (the server), and brings back your food (the response). You never need to know how the kitchen works — you just need the menu.

What is REST?

REST stands for Representational State Transfer. It is an architectural style, introduced by Roy Fielding in 2000, that defines a set of constraints for building web services. An API that follows these constraints is called a RESTful API.

The key ideas of REST are:

  • Client–server separation — the frontend and backend are independent.
  • Statelessness — every request contains all the information the server needs. The server does not remember previous requests.
  • Resources — everything is a resource (a user, a product, an order), identified by a URL like /users/42.
  • Standard HTTP methods — GET to read, POST to create, PUT/PATCH to update, DELETE to remove.
  • Representations — resources are usually sent as JSON.

A real example

When you open a weather app, it calls something like:

GET https://api.weather.com/v1/cities/mumbai/forecast

The server responds with JSON data, and the app renders the forecast on the screen.

Why REST APIs matter

  • Every major platform — Google, YouTube, Instagram, payment gateways like Razorpay and Stripe — exposes REST APIs.
  • Mobile apps and web frontends talk to their own backends through REST.
  • Microservices inside companies communicate over REST.

What you will learn in this course

HTTP methods and status codes, JSON request/response bodies, headers, authentication (API keys and JWT), CRUD API design, pagination, versioning, error handling, security best practices, and testing APIs with tools like Postman and curl.

In the next lesson, we will look at how the HTTP protocol actually works under the hood.