APIs and JSON Basics
How different programs talk to each other, and the format they usually use to send each other data.
Last updated: September 23, 2026
What is an API
API
Short for Application Programming Interface, a defined interface through which two programs can exchange data, without either one needing to know how the other is built internally.
Everyday example
A weather app asks a weather service's API for the current values for a location, instead of running its own weather stations.
Web API
An API reachable over the internet via HTTP, by far the most common kind of API today.
HTTP methods
Determine what should happen to the data on the server.
The most important methods
GETRequests data, doesn't change anything on the serverPOSTSends new data to the server, for example creating a new accountPUTReplaces existing data entirelyDELETEDeletes data on the serverMatching status codes
After every request, the server responds with a status code like 200 or 404. A full overview is on the dedicated status codes page.
JSON
JavaScript Object Notation, a simple text format most APIs use today to send their data.
Basic building blocks
{ }Curly braces wrap an object, a collection of named values[ ]Square brackets wrap a list of several values"key": "value"A named value, keys and text sit in quotation marks"number": 5Numbers are written without quotation marksExample
{ "name": "Max", "age": 20, "city": "Berlin" }A simple JSON object with three values