HollowEngine is a content creation engine for Minecraft. It combines Kotlin scripting, visual programming, and tools for building NPCs, events, gameplay systems, and interactive experiences.

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• In-game IDE with syntax highlighting, code analysis, dockable tool windows, an embedded game viewport, a console (commands and Kotlin), and file previews
• Kotlin Scripting with full access to the game's classes without having to re-enter the game, including client/server-side scripts, startup scripts, shared scripts, and .mixin.kts mixin scripts
• Optional Narrative addon with visual story graphs, dialogues, resumable Kotlin stages, and cutscenes
• Advanced model system (.gltf, .glb, .obj, .fbx, .bbmodel, .geo.json)
• Animator with layers and a visual state graph editor
• VFX system with a particle editor, renderers, sub-emitters, glow, and sky effects
• Shader graph: node-based .material editor connected to VFX and previews
• Advanced UI framework that includes a Compose-like DSL, a CSS-like styling system (HSS with imports and theme variables), 3D transformations, masks, effects, and a reusable node graph canvas
• NPC tooling with models, textures, animations, interactions, and trades
• Scene and camera tooling for cinematic workflows
• Embedded asset, resource pack, and datapack loading
• Addons in a universal jar (Fabric and NeoForge), including addons embedded in other mods, and project import/export
• MCP server addon that lets AI agents inspect and drive the running game

• Minecraft 1.21.1
• Fabric
• NeoForge
• Kotlin 2.4.0

• runtime/: main engine, UI, gameplay integration, tests
• bridge/: shared compatibility layer (bootstrap <---> bridge <---> runtime)
• bootstrap/: shared bootstrap code and resources
• bootstrap-fabric/: Fabric bootstrap implementation
• bootstrap-neoforge/: NeoForge bootstrap implementation
• addons/compiler/: scripting compiler addon
• addons/narrative/: story graphs, dialogue, and cutscene addon

1. Install the HollowEngine jar into your mods/ folder. One jar covers both Fabric and NeoForge.
2. If you use scripting, install HollowEngineCompiler-*.jar as well. Addons work from mods/ like any other mod, or from hollowengine/addons/ if you prefer to keep them apart. If both folders contain the same addon id, the newest version is selected at startup.
3. For stories and cutscenes, install HollowEngineNarrative-*.jar and add hollowengine-narrative to Depends on addons in the project settings.
4. Start Minecraft.
5. Open the in-game editor and begin creating content.

Use the Gradle wrapper from the repository root:

• .\gradlew.bat buildAndCollect - build enabled bootstrap platforms and collect outputs into merged/
• .\gradlew.bat test - run JVM tests
• .\gradlew.bat buildAddons - build and collect every addon, including the compiler
• .\gradlew.bat developmentJar - build build/development/HollowEngine-<minecraft>-<version>-dev.jar for compiling external addons

build also produces the development jar, and buildAndCollect copies it into merged/. It exposes engine classes (including common.addons and UI), the bridge, and bundled libraries directly on the compile classpath. Use it as compileOnly with Mojang/Parchment mappings and the Kotlin version used by HE. Install the regular universal jar in the game; the development jar is only for compilation.

For an addon tied to a mod, use the addon template. Its entrypoint is compiled into the mod jar and HE activates it only when that mod is installed. Independent addons continue to use the separate format-3 jar.

This project is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.