REST vs Websockets

Idem can be accessed through either REST or Websocket connections.

When to use REST?
Only recommended for initial setup, prototyping and logical testing (see 5 minute matchmaker). Simple to implement but limited on throughput performance.
For specification, please see REST API Specification

When to use Websockets?
To be used for all production systems with significant usage.
For specification, please see Websocket API Specification