Stop 23 · Interview PreparationTechnical · 4/8

HTTP & REST fundamentals

In short

Status codes, idempotency, headers, caching: interviewers use these to check you really understand the web, not just your framework. They're quick wins if you prepare.

Fluent, fast recall of HTTP methods, status codes, and REST conventions — frequently tested as quick-fire questions or embedded in take-home API design tasks.

The purple blob hands a stamped envelope to a post office clerk who gives back a receipt.

Think of it like this

Sending a parcel at the post office

The envelope has an address (URL), a service type like speed post (method), stamps and labels (headers) and the letter inside (body). The counter hands you a receipt (status code) saying accepted, rejected or wrong address.

Watch it happen

One resource, many conversations

Client

API

POST /orders

1/8Create a new order. POST is not idempotent: sending it twice can create two orders.

The big ideas

What you need to know

Safe and idempotent

GET is safe. GET, PUT and DELETE are idempotent: repeating them gives the same result. POST usually isn't.

Status code families

2xx success, 3xx redirect, 4xx client mistake, 5xx server failure. Know 200, 201, 204, 304, 400, 401, 403, 404, 409, 429, 500 and 503.

Headers do real work

Content-Type, Authorization, Cache-Control, ETag and Location carry meaning. Name a few with their purpose.

REST is stateless

Each request carries everything needed, like the auth token. That's what lets you add servers freely.

See it in code

Walk through the code

http

1POST /api/orders HTTP/1.12Host: api.shop.dev3Content-Type: application/json4Authorization: Bearer eyJhbGciOi...5Idempotency-Key: 8f14e45f-ea7c-4e1b6 7{ "productId": 42, "quantity": 2 }8 9HTTP/1.1 201 Created10Location: /api/orders/98111Content-Type: application/json12 13{ "id": 981, "status": "pending_payment" }