JSON-RPC

It is similar to the XML-RPC protocol, defining only a few data types and commands.

JSON-RPC works by sending a request to a server implementing this protocol.

The client in that case is typically software intending to call a single method of a remote system.

[1] A request is a call to a specific method provided by a remote system.

Although <-- is often called a response in client–server computing, depending on the JSON-RPC version it does not necessarily imply an answer to a request.