What Is an API? REST APIs Explained Simply
Understand APIs and REST — how websites and apps communicate. With real-world examples from Razorpay, Google Maps, and Twitter.
What Is an API?
API stands for Application Programming Interface. In simple terms, an API is a set of rules for how two pieces of software communicate with each other.
The classic waiter analogy: A restaurant kitchen (the system with data) does not talk directly to diners (the user's app). The waiter (the API) takes orders from diners, brings them to the kitchen, and returns with the food. The diner does not need to know how the kitchen works — just how to order.
Real Examples of APIs You Use Daily
Google Maps API: When you use Swiggy or Zomato and see a map showing your delivery location, that map is powered by the Google Maps API. Swiggy does not build their own maps — they use Google's via API.
Razorpay/PayU payment API: When you checkout on an e-commerce site and see a payment page, that is a payment gateway API. The e-commerce site sends your order to Razorpay via API; Razorpay handles the actual payment.
Weather API: Any weather app on your phone gets data from a weather API (like OpenWeatherMap or IMD). They do not have their own weather satellites.
SMS/OTP API: When you receive an OTP from a website, the website used an SMS API (Twilio, MSG91, Fast2SMS) to send it.
What Is a REST API?
REST (Representational State Transfer) is the most common architectural style for web APIs. REST APIs use standard HTTP methods:
GET: Retrieve data (list of products, user profile)
POST: Create new data (place an order, submit a form)
PUT/PATCH: Update existing data (edit profile, modify order)
DELETE: Remove data (delete account, cancel order)
REST APIs communicate using JSON format for data exchange.
How to Test an API
Postman is the standard tool for testing and exploring APIs. You can:
Enter an API endpoint URL
Select HTTP method (GET, POST, etc.)
Add authentication headers
Send request and see JSON response
Frequently asked questions
What is the difference between an API and a website?
A website is designed for humans — it has a visual interface (HTML, CSS). An API is designed for software — it returns raw data (usually JSON) that an app processes and displays its own way. Both run on servers and respond to HTTP requests.
What is REST API?
REST is an architectural style for APIs that uses standard HTTP methods (GET, POST, PUT, DELETE) and typically returns JSON data. It is stateless — each request contains all information needed without depending on previous requests.
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