What is an API?
Quick answer
An API (application programming interface) is a set of rules that lets one piece of software request data or actions from another. When a weather app shows today’s forecast, it’s usually asking a weather service’s API for the data, then displaying the answer.
The restaurant analogy
Think of a restaurant. You (an app) want food (data), and the kitchen (another system) can make it. You don’t walk into the kitchen; you give your order to a waiter, who takes it to the kitchen and brings back your dish. The API is the waiter: a defined way to ask for something and get a response, without needing to know how the kitchen works.
Everyday examples
| You do this | Behind the scenes |
|---|---|
| Check the weather on your phone | The app calls a weather service’s API |
| Click “Sign in with Google” | The site uses Google’s login API |
| Pay online with a card | The shop sends the payment through a payment provider’s API |
| See a map on a restaurant’s website | The page uses a maps API |
| Ask an AI assistant inside another app | The app sends your request to the AI provider’s API |
How web APIs work
Most modern APIs run over the web:
- An app sends a request to a web address called an endpoint, for example asking for the weather in Paris.
- The request often includes an API key, a password-like code that identifies the app.
- The server sends back a response, usually in a format called JSON, which looks like this:
{"city": "Paris", "temp_c": 14}. - The app turns that data into something you can see.
A common style for web APIs is REST, which uses ordinary web actions like GET (fetch data) and POST (send data).
Why APIs matter
- No need to rebuild everything. A small app can add maps, payments or translation by connecting to existing services.
- Security. The API only exposes what the provider chooses, not its whole system.
- Automation. APIs let programs work together without a person copying data between them.
Want to start using APIs yourself? Here’s how to learn coding online for free, and how AI tools use them.
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