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Identity & API Security Track 0 · The Absolute Basics
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THE ABSOLUTE BASICS · LESSON 4

What is an API? And what is JSON?

Every app on your phone talks to the internet. It checks the weather, loads messages and shows flight prices. It does this through APIs. Your goal: read a simple API request and its JSON answer.

Key points
  • An API is a menu of things one program does for another.
  • It uses the same HTTP as websites, but it returns data, not a page.
  • The data is usually JSON: keys and values.
  • A real API asks for proof first, like an API key or a token.

An API is a menu

An API (Application Programming Interface) is a list of requests that one program lets another program make. It uses the same ask-and-answer HTTP from lesson 2. There is one difference. The response is not a page for your eyes. It is data for a program to use.

Think of it like…

ordering at a restaurant. The menu lists the dishes you may ask for. These are the API's endpoints. The waiter carries your order to the kitchen and brings food back. That is the API. You never enter the kitchen.

JSON: the note the waiter carries

An API usually sends data in a format called JSON. It looks like this: {"name": "Maya", "seat": "12A"}. Curly braces { } wrap the whole note. Inside are "key": value pairs, separated by commas. The key names a thing ("seat"). The value is the answer ("12A"). A list goes in square brackets [ ]. That is almost all of it. People read JSON easily, and programs like it because it is predictable.

A tiny flight API

Say an airline offers an API. It receives a request and sends a response. Its menu of endpoints might look like this:

RequestWhat it doesWhat comes back (JSON)
GET /flightsList all flights[{"id":42,"to":"Cairo"}, …]
GET /flights/42Details of flight 42{"id":42,"to":"Cairo","gate":"B12"}
POST /bookingsBook a seat{"booking":"B-771","seat":"12A"}

Remember: GET reads and POST creates. Your phone app sends many small requests like these. It gets JSON back and turns it into buttons and lists.

📱 Phone app🤖 Bot AAPI(the waiter)Database(the kitchen)GET /flightsGET /flightslook it up✗ no key → 401 "who are you?"[{ "flight": 42, "to": "Cairo" }]the answer is DATA (JSON), not a web page
Figure — One kitchen, many customers. Your phone app and Bot A send simple requests to the same API. The API looks the answer up in the database behind it and sends back a small piece of JSON. This is data, not a page. A request with no key is turned away at the door.
Story time

Kai, an AI agent, wants tomorrow's flights to Cairo. It does not open a website like a person. It calls GET /flights and reads the JSON list at once. Bot A, an automated helper, does the same on another endpoint. Neither sees a web page. That is how software talks to software.

Watch out

An API that answers every stranger is dangerous. So real requests carry a secret that proves the caller may ask. It is an API key or a token. You will meet them soon (API keys vs tokens and what a token is). For now remember: no proof, no answer.

🧪 Interactive lab — enable JavaScript to play with this one.

🧪 Try it free

Look at a real API menu that programs can read, with GraphQL Check.