An API, short for application programming interface, is a set of rules that lets one piece of software ask another for data or for an action. When a weather app shows today’s forecast, it does not own a weather station. It asks a weather service through an API and displays the answer.
The restaurant analogy #
Think of a restaurant. You (the client) read the menu, tell the waiter what you want, and the kitchen (the server) prepares it. You never walk into the kitchen. The waiter is the API: a defined way to make requests and get responses, without knowing how the kitchen works.
How a web API request works #
Most web APIs use HTTP, the same protocol your browser uses. A request has four main parts:
- A URL, which says what you are asking for, such as a list of products.
- A method, which says what you want to do. GET reads data, POST creates it, PUT or PATCH changes it and DELETE removes it.
- Headers, which carry details such as the data format or an access key.
- A body, which holds the data you send when creating or updating something.
The server replies with a status code and usually some data, most often in JSON. A code in the 200s means success, 400s mean the request had a problem and 500s mean the server failed.
What JSON looks like #
JSON is plain text that describes data as names and values:
- A product might have a name, a price and a list of tags.
- Lists are written in square brackets and objects in curly braces.
If you ever need to read a messy response, a JSON formatter makes it easy to scan.
Authentication and keys #
Many APIs need to know who is calling. The usual ways are an API key sent in a header, or OAuth, where a user grants your app limited access. Treat keys like passwords: keep them out of public code and rotate them if they leak.
Rate limits #
Providers cap how many requests you can make per minute or per day. If you hit the limit you will get a 429 status code. Cache responses you reuse and back off before retrying.
Try it yourself #
- Pick a free public API that needs no key, for example a public data or joke API.
- Open its documentation and find a GET endpoint.
- Paste the URL into your browser or call it with a tool such as curl.
- Read the JSON that comes back and note which fields you could use.
Why APIs matter #
APIs let teams build faster, because payments, maps, email and AI features can be added without rebuilding them. They also let systems you control talk to each other cleanly. Understanding requests, responses and status codes is one of the most useful skills for any developer.
