What is an API?

API stands for Application Programming Interface.

An API is a way for different software applications to talk to each other. It defines the rules for how one piece of software can request data or functionality from another piece of software.

Think of it like an ATM machine. You can check your balance, withdraw cash, or deposit money, but you don’t see or understand all the complex banking systems working behind the scenes. You just use the interface the ATM provides. An API works the same way.

The most common type you’ll hear about is a web API (or REST API). This is when your application makes requests over the internet to get or send data. You’ll also hear terms like “GraphQL API” or “public API.” These describe different styles or access levels of APIs, but they all serve the same basic purpose. When you use a weather app on your phone, it’s calling a weather API to get the current temperature and forecast.

For example, if you wanted to get weather data, you might make an API call to something like https://api.weather.com/current?city=Chicago. The API would send back data (usually in JSON format) with the current weather information.

APIs are everywhere in modern web development. When you build a Single Page Application, the frontend uses AJAX to call APIs to get and update data. When you integrate with services like Stripe for payments, Google Maps for location data, or Twitter for social media, you’re using their APIs.

But the term API is much older than the web and can also refer to the functionality or interface offered by a software library. For example, the JavaScript Array API includes methods like slice(), map(), and filter(). These are the functions the Array object provides for you to work with arrays. You don’t need to know how they’re implemented internally, you just need to know what they do and how to call them.