What HTTP methods do you know? What is idempotency?

Main HTTP methods:

• GET — retrieve data from the server.
• POST — send data to the server to create a resource.
• PUT — replace an existing resource or create it if it does not exist.
• PATCH — partially update a resource.
• DELETE — delete a resource.
• HEAD — get only the response headers without the body.
• OPTIONS — find out which methods are supported for a resource.

Idempotency — a property of an operation where multiple identical requests produce the same result as a single request. In HTTP, methods GET, PUT, DELETE, HEAD, OPTIONS are considered idempotent, while POST is not. This is important for reliability and repeatability of requests without side effects.