The method tells the server what to do whilst additional parameters can be passed via the params key.
Receiving A Response
As soon as the server finishes handling a request, a response will be sent back to the client. This response will carry the same ID as the request, so the client can match the received response to the original request it sent. A response could look something like the following:
The methods available for use in the method key are determined by the commands exposed by the core, which can be found here. Each command symbolizes a method. The parameters it supports can be found in the execute method (at some point in the future actual wiki documentation for these might be added).
Why Not Use The Microsoft Language Server Protocol Altogether?