What are the differences between the HEAD, GET, POST, and PUT methods in HTTP?

• HEAD: Requests headers that would be obtained using the GET method, but without a response body. Useful for checking resource existence or obtaining metadata. Idempotent and safe.
• GET: Requests a representation of the specified resource. Used for data retrieval. Idempotent and safe.
• POST: Sends data to be processed to the specified resource. Data is included in the request body. Used for creating a new resource or submitting form data. Unsafe and not idempotent (repeated requests may lead to duplicates).
• PUT: Sends data to update or create a resource at the specified URI. If the resource does not exist, the server may create it. Data is included in the request body. Idempotent (repeated requests do not change the server state after the first successful request). Unsafe.

Key differences:

Method	Purpose	Request body	Response body (usually)	Idempotent	Safe
HEAD	Get headers	No	No	Yes	Yes
GET	Retrieve resource	No (usually)	Yes	Yes	Yes
POST	Send data	Yes	Yes	No	No
PUT	Update/create resource	Yes	Yes	Yes	No

Safe means the request does not change the server state. Idempotent means that multiple executions of the same request lead to the same result on the server.