The idea
Resource URLs identify entities or collections. GET retrieves without intentionally changing server state, POST commonly creates or requests processing, PUT can replace a resource and DELETE removes it. Idempotence concerns the intended server effect of repeated equivalent requests, not whether every response is identical.
Worked example
GET /courses/42 retrieves a fictional course. DELETE /saved-courses/42 removes a saved entry; a repeated delete may return a different status while the intended final absence stays the same. Repeating an unprotected create request can instead produce duplicate resources.
Try it
Design collection and individual URLs for fictional notes. Choose methods for listing, creating, replacing and deleting. Explain which repeated operations should have the same intended effect and why that does not require identical response bodies.