What Is an API and Why Does Every App Use One?

If you’ve spent any time in tech, you’ve heard the word API thrown around constantly. What is an API? It stands for Application Programming Interface, but that definition doesn’t help much. Let me explain it in a way that actually makes sense.

The Restaurant Analogy

Imagine you’re at a restaurant. You don’t walk into the kitchen and cook your own food. Instead, you talk to a waiter — you tell them what you want, they go to the kitchen, and they bring back what you ordered.

An API is the waiter. It sits between you (the client) and the kitchen (the server/database). You make a request using the API’s defined menu (its endpoints), and it brings back the data.

A Real Example

When you open a weather app on your phone, the app doesn’t have its own weather satellites. It sends a request to a weather API like this:

GET https://api.weather.com/current?city=Dhaka

The API responds with weather data in JSON:

{
  "city": "Dhaka",
  "temperature": 32,
  "condition": "Sunny",
  "humidity": 65
}

The app reads this JSON and displays it nicely. The weather service provides the data; the app provides the interface. They’re connected by an API.

Why APIs Are Everywhere

APIs allow different software systems — built in different languages, running on different servers — to communicate using a shared standard. That’s why:

• Instagram can let you “Sign in with Google” (Google’s OAuth API)
• Shopify can accept payments (Stripe’s API)
• Your portfolio can show your GitHub repos (GitHub’s API)
• Delivery apps can show your location on a map (Google Maps API)

Types of APIs

• REST APIs — the most common; use HTTP and JSON
• GraphQL — lets clients request exactly the data they need
• WebSocket APIs — real-time, two-way communication (chat apps, live feeds)
• Third-party APIs — Stripe, Twilio, SendGrid, etc.

Conclusion

What is an API? It’s a defined way for software to talk to other software. Every modern app you use relies on APIs — for authentication, payments, maps, data, and more. As a developer, you’ll both consume existing APIs and build your own. Understanding what they are is the first step.

Read next: What Is a REST API? Plain-Language Explanation

External resource: MDN — Introduction to Web APIs