The kdeconnect protocol:

Communication between heterogenous devices is achieved using NetworkPackages.
NetworkPackages are independent and self-contained pieces of information that
are sent from one device to another serialized in json.

The basic structure of a NetworkPackage is the following:

{
    "id": 123456789,
    "type": "org.kde.whatever",
    "body": {

    },
    "version": 1
}

Each type of package defines what it should contain inside its "body", so only
the sender and receiver of this type of package need agree about it.