What is idempotency? Can you explain with examples of HTTP methods?

Idempotency is a property of an operation where performing it multiple times yields the same result as performing it once.

In the context of HTTP methods:

• GET — is idempotent, as a request to retrieve a resource does not change the server's state, and repeated requests return the same result.
• PUT — is idempotent, because updating a resource with the same data multiple times results in the same state.
• DELETE — is idempotent, as deleting a resource multiple times will not change the result after the first deletion (the resource is already deleted).
• POST — is not idempotent, as each request usually creates a new resource or changes the server's state, and repeated requests can lead to different results (e.g., multiple records created).

Example:

PUT /users/123
{
  "name": "Ivan"
}

If this request is performed multiple times, the user with id 123 will have the name "Ivan" — the state does not change after the first request.

Thus, idempotency is important for the reliability and predictability of APIs, especially when repeated requests are made due to network failures.