REST API

REST (Representational State Transfer) is an architecture style for APIs. An API that follows this style is called RESTful. The core idea: everything is a resource with its own address, manipulated through the verbs HTTP already offers.

The methods

So GET /contacts/42 fetches contact 42 and DELETE /contacts/42 removes it. The address says what; the method says the action.

The status codes you will run into

• 2xx — it worked (200 ok, 201 created).
• 4xx — the error was on the requester's side: 401 no credentials, 403 no permission, 404 does not exist, 429 rate limit exceeded.
• 5xx — the error was on the server's side. Here, retrying the call usually makes sense; on a 4xx, it does not.

Stateless — and why it matters

REST is stateless: every call carries everything it needs, and the server does not keep memory between one call and the next. This simplifies scaling, but it means authentication goes on every request.

REST, SOAP and GraphQL

• SOAP — older, XML-based, more rigid and verbose. Still common in banks and legacy systems.
• GraphQL — the client describes exactly the fields it wants, in a single call. Avoids fetching too much data.
• REST — the dominant standard for web integrations, including the WhatsApp API.