StemStudio

A browser-based 3D sandbox editor and runtime. Build, script, and play 3D games in your browser. Open source under MIT.

StemStudio gives you a complete authoring environment — scene editor, behavior scripting in JavaScript, physics, multiplayer, an AI copilot — that runs entirely on your machine. Projects live in your browser (IndexedDB) or in a folder you pick (File System Access API). No accounts, no cloud, no lock-in.

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Features

• 3D scene editor built on Three.js — primitives, materials, transforms, scene tree, viewport, gizmos.
• Behaviors — JavaScript classes attached to scene objects with a lifecycle (init, update, onCollision, etc.) and a built-in pack covering input, character controllers, vehicles, AI NPCs, UI, audio, and more.
• Lambdas — an entity-component system on top of behaviors when you need archetype-driven, batched work.
• In-editor code editor — Monaco for behavior and script authoring with full TypeScript-style assist.
• Physics — Ammo.js / Rapier integration with rigid bodies, joints, raycasting.
• Local multiplayer — Colyseus sidecar auto-spawned on bun run dev. Two browser tabs on the same machine join a real room.
• AI copilot (BYOK) — bring your own keys for Anthropic, OpenAI, Meshy (3D model gen), ElevenLabs (TTS), and AnythingWorld. Configure once, use everywhere.
• Local-first persistence — IndexedDB for seamless auto-save, or open a real folder via File System Access API (Chromium) for git-friendly workflows.
• Export & share — package any project as a standalone static site (Player-only build) you can host anywhere.

Quick start

Prerequisites: Bun 1.0+, Go 1.21+, Node.js 20+.

git clone https://github.com/your-org/stemstudio.git
cd stemstudio
git submodule update --init --recursive
bun install
bun run dev

That single command starts three processes:

• Vite on http://localhost:5173 — the editor.
• AI server on http://localhost:8081 — proxies AI calls to providers using your keys.
• Multiplayer sidecar on ws://localhost:2567 — Colyseus rooms for local multiplayer.

Open http://localhost:5173 and follow the first-time bootstrap modal to pick your project storage mode (IndexedDB or local folder).

To use AI features, add a .env file (copy from .env.example) with whichever provider keys you want:

ANTHROPIC_API_KEY=sk-ant-...
OPENAI_API_KEY=sk-...
MESHY_API_KEY=...
ELEVENLABS_API_KEY=...
ANYTHING_WORLD_API_KEY=...

Any key you omit makes that provider unavailable — the editor will prompt you for it when you first try a feature that needs it.

What's in the box

• Editor, player, runtime, behaviors, lambdas, physics, rendering, scheduler, asset loading.
• Monaco-based script/behavior editor.
• Local multiplayer Colyseus sidecar.
• AI proxy server (Go) that forwards calls to your provider keys.
• BYOK key management — keys stay in your browser's IndexedDB and are only sent to the provider you configured.
• Build tooling (Vite, TypeScript, ESLint, Bun test).
• Engine docs alongside the code: behaviors, lambdas/ECS, physics, UI, art specs.

Documentation

• Architecture overview — how the editor, AI server, and multiplayer sidecar fit together.
• BYOK setup — connect your AI provider keys.
• Multiplayer guide — local sidecar and self-hosted deployment.
• Exporting a game — package a Player-only static site.
• Contributing — development workflow and PR guidelines.

Deeper engine docs (behaviors lifecycle, lambdas/ECS, physics, scheduler, rendering) live under docs/ in this repo.

Development workflow

This project uses Bun as its package manager and task runner.

bun run dev            # All-in-one: Vite + AI server + MP sidecar
bun run dev:editor     # Editor only (Vite)
bun run dev:ai         # AI server only
bun run dev:mp         # MP sidecar only

bun run build          # Production static build
bun run typecheck      # TypeScript verification
bun run test           # Unit + integration tests
bun run lint           # ESLint

To export a single project as a Player-only static site, use the in-editor File → Export game action and follow the instructions in docs/exporting-a-game.md.

Browser support

• Chromium-based (Chrome, Edge, Brave, Arc): full feature set including File System Access API for folder-based project storage.
• Firefox: full feature set with IndexedDB storage only (no folder access).
• Safari: full feature set with IndexedDB storage only (no folder access).

WebGL2 is required. WebGPU support is experimental and opt-in.

Contributing

We welcome contributions. Please read CONTRIBUTING.md before opening a PR.

Bug reports, feature requests, and discussions: GitHub Issues.

License

MIT. See THIRD-PARTY-NOTICES.md for the licenses of bundled dependencies.

Security

Found a vulnerability? Please don't open a public issue. See SECURITY.md for private disclosure.

Acknowledgements

Built on Three.js, React, Vite, Colyseus, Monaco Editor, Ammo.js, Rapier, and Bun.