Which HTTP methods are considered idempotent and why?

Idempotent HTTP methods are those that can be executed multiple times in a row without changing the result after the first call. These methods include:

• GET — retrieving a resource does not change the server's state.
• PUT — updating a resource with specified content; repeated calls with the same data do not change the result.
• DELETE — deleting a resource; repeated calls delete the resource if it exists, and the state remains unchanged.
• HEAD — similar to GET but without a response body; does not change the state.

The rationale for idempotency is that repeated calls with the same parameters do not cause additional changes on the server, which is important for reliability and retrying requests in case of network errors.