Http idempotent methods

An Http method is idempotent when one or more repetitive request (same request) makes no further impact to server after first request.

Like repetitive GET request makes no impact hence its a idempotent method. The other idempotent methods are PUT and DELETE.

POST is not a idempotent method - First request will insert a record and further same request will add further more records.

PATCH can be idempotent but not necessarily hence it is not safe - It depends upon the implementation, how you are updating the property.