Feels very similar to JSON RPC.

This isn't a script at all but a way to call an RPC method. And over a non duplex connection at that.

I often use something very similar with a few additions to support callbacks. Add an ID field so that responses can be matched and you suddenly support calls being made over a duplex connection such as Websocket or TCP connection;

Shorthand and longhand formats complicate things so stick with one type. The whole $ prefixed params are also un-needed, especially if your'e expecting them and have the important values under your own expected keys anyway.

But then after all this you start turning into json-rpc.