mc-addons-boilerplate
Minecraft UI.json Documentation
Docs are in the Wiki. Contribute what you want to using Issues: start with [Edit] (for direct edit suggestions, i.e. change "jason" to "json") or [Suggestion] (for ideas with contents, i.e. this type exists).
NOTE: There is some official documentation now for this. Soon, HTML5-based GUIs can be created! This repository will stay around for the JSON-based UI documentation and some boilerplates and examples for Minecraft GUIs and other addons.