Bazecor-API is a SDK, kinda: https://github.com/Dygmalab/bazecor-api
You can also contribute to Bazecor to add features you want, it's open-source! 😊 https://github.com/Dygmalab/Bazecor
You can also check the Focus plugin docs. It's the Kaleidoscope plugin that implements the bi-directional communication protocol that Bazecor uses to talk to the keyboard https://github.com/keyboardio/Kaleidoscope/blob/master/docs/plugins/FocusSerial.md#wire-protocol