Addon-Workspace | Hyperium uses a system called addons

To get started, first you want to either clone or download the addon workspace from here, open it in an IDE that supports Java or Kotlin (preferably IntelliJ), and import the build.gradle file. Likely, at first you won't have access to the decompiled Minecraft code. To fix this, all you have to do is open the Gradle tab on the right side of your screen. Open the dropdown menu, Tasks, forgegradle, and run setupDecompWorkspace. After this, refresh your gradle deps using the button that looks like two arrows spinning around eachother. Once you've done that, you can open Tasks, forgegradle, and run genIntellijRuns. This is going to create the base for running the client once you're ready to test something. Test to see if it setup properly by going into the top right and seeing a dropdown menu saying Minecraft Client, beside that is a green arrow. Press the arrow, if it starts up, you're all good, otherwise, click on the dropdown menu, and where it says Use classpath of module: %WORKSPACE_NAME%, you will want to change that to be %WORKSPACE_NAME%.main. An example of this would be ExampleAddon.main. At this point, you should be good to go. If you wish to login to your account to test something on a server, open the dropdown menu saying Minecraft Client, and insert --username (username/email) --password (password) then run the client.