I made a Client API for GaiaOnline back in 2015 to use in a bunch of private modifications. I don't play GaiaOnline much anymore so I've recently updated the code and made a Repository on GitHub for other people to use.

GaiaOnline API Repository

Here is a small UserScript that uses this API. I made this UserScript as an example/guidelines for people using the API.

Here is a screenshot of a Private Modification I made using this API

I hope some of you find this code useful and enjoy making mods with it.