How to distinguish between GET and POST methods when developing REST API and in which situations are they used?

GET and POST methods are two main HTTP methods used in REST API, with different purposes:

• GET is used to retrieve data from the server. It should be idempotent and not change the server's state. GET requests can be cached and may be cached by the browser.

• POST is used to create new resources or perform operations that change the server's state. POST requests are not idempotent and usually contain a body with data.

When to use:

• GET — when you need to get data, such as a list of users or details of a specific object.
• POST — when you need to create a new object, submit a form, or perform an action that changes data.

Example:

GET /users/123 HTTP/1.1

POST /users HTTP/1.1
Content-Type: application/json

{
  "name": "Ivan",
  "email": "ivan@example.com"
}

In testing, it is important to verify that GET requests do not modify data, and POST requests correctly create or modify them.