HTTP & APIs
API
An API is a defined contract that lets one software component request data or actions from another without knowing its internal implementation.
Diagram
Mobile App ──▶ [API Contract] ──▶ Backend Server
(endpoints + rules) (hidden internals)
Client only sees: GET /users, POST /orders
Client never sees: database schema, business logicIn Depth
API stands for Application Programming Interface. A web API exposes a set of endpoints and rules that external clients (mobile apps, other services, third-party developers) use to read or modify data.
Code Example
Calling a public API
const response = await fetch('https://api.stripe.com/v1/charges', {
method: 'POST',
headers: { 'Authorization': 'Bearer sk_live_...' },
body: JSON.stringify({ amount: 2000, currency: 'usd' }),
});
const charge = await response.json(); // 201 CreatedCommon Misconception
An API is not the same as a database. The API is the controlled front door; the database is the private storage room behind it. Clients should never connect to the database directly.
Real World Usage
Stripe's payment API, GitHub's repo API, and Twitter's timeline API power thousands of third-party apps — all through HTTP endpoints.