Before talking about reliability, we need to define which HTTP methods are safe and which are idempotent in the REST context. So, let's first define what safe and idempotent methods are:

• An HTTP method is considered to be safe provided that, when requested, it does not modify or cause any side effects on the state of the resource
• An HTTP method is considered to be idempotent if its response stays the same, regardless of the number of times it is requested, am idempotent request always gives back the same request, if repeated identically.

The following table lists which HTTP methods are safe and which are idempotent:

Consumers should consider operation's safety and the idempotence features in order to be served reliably.