API

About

An API (Application Programming Interface) is a way for different software systems to talk to each other. It defines rules and protocols that allow applications to request and exchange data.

We can think of an API as a waiter in a restaurant:

• We (the client) tell the waiter (API) what we want (a dish).

• The waiter goes to the kitchen (server) and brings our food (data).

• We don’t need to know how the kitchen works. We just get our dish.

How APIs Are Used in Applications ?

APIs are used in almost every modern application to communicate between systems, fetch data, send user inputs to a server, or connect with third-party services. Whether we are using a web application, mobile app, desktop software, or even IoT devices, chances are APIs are involved.

1. APIs Connect Frontend and Backend

When we open a mobile or web application, what we see on the screen is the frontend (user interface). However, the real data—like our profile, messages, transactions, or orders—lives in the backend (server and database). To access that data, the frontend sends API requests to the backend.

Example: In a shopping app

• When we tap “My Orders,” the frontend sends a request to an API endpoint like: /api/orders/user/123

• The backend receives the request, fetches data from the database, and sends it back.

• The frontend then displays that order information to we.

2. APIs Power User Actions

Every meaningful action a user performs—like logging in, signing up, searching, saving, or deleting—results in an API call.

Examples:

• Login: Sends username and password to the POST /login API

• Search: Sends keywords to the GET /products?query=laptop API

• Add to Cart: Sends product ID to the POST /cart/add API

In all of these, the UI just provides a form or button, but the action is performed by calling an API.

3. APIs Connect to External Services

Applications rarely work in isolation. They often depend on third-party systems. APIs allow our app to integrate with these systems easily.

Examples:

• Using Google Maps API to show a location

• Using a payment gateway API (like Stripe or Razorpay) to process payments

• Using SMS or Email APIs (like Twilio, SendGrid) to send messages or OTPs

Our system doesn't have to rebuild these features—it just consumes existing APIs.

4. APIs Enable Mobile/Desktop Apps to Work Just Like Web Apps

When we use a mobile app, it may not have its own internal logic or database. Instead, it works like a thin client—sending requests to a centralized backend through APIs.

This makes it easier to:

• Keep logic consistent across platforms (web, mobile, desktop)

• Centralize data management

• Update the backend without needing to change each client app

5. APIs Help Microservices Communicate

In large backend systems, different modules may be split into microservices. For example:

• One service handles users

• Another handles orders

• Another handles payments

These services talk to each other via internal APIs. It makes the system modular, easier to scale, and maintainable.

6. APIs Enable Automation and Integration

APIs are not just for user-facing apps. Many systems use APIs to:

• Automate tasks (e.g., triggering builds or reports)

• Integrate with other systems (e.g., CRM or ERP tools)

• Export/import data between platforms

For example, an e-commerce platform might push order updates to a logistics provider through an API.