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.

Sponsor this project

If StemStudio is useful to you or your organization, please consider sponsoring its continued development. Sponsorships fund maintenance, new features, documentation, and community support.

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 / Tripo / Rodin (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+. New machine? See Setting up your dev environment for per-OS install steps (macOS, Windows, Linux).

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.

Setting up your dev environment

You need three tools on your PATH: Bun 1.0+ (package manager + task runner), Go 1.21+ (the AI proxy server), and Node.js 20+ with npm (the multiplayer sidecar). Pick your OS below, then continue with Quick start.

macOS

Using Homebrew:

brew install oven-sh/bun/bun go node git

Or install each from its official site (links above). Apple Silicon and Intel are both supported.

Linux

# Bun
curl -fsSL https://bun.sh/install | bash

# Node.js 20+ — via nvm (recommended; distro packages are often older)
curl -fsSL https://raw.githubusercontent.com/nvm-sh/nvm/v0.40.1/install.sh | bash
nvm install 20

# Go 1.21+ — prefer the official tarball; distro `golang-go` may lag
#   https://go.dev/doc/install   (or: sudo apt install golang-go / sudo dnf install golang)

# Build essentials for any native dependency compilation
sudo apt install -y build-essential git    # Debian/Ubuntu
# sudo dnf groupinstall "Development Tools"  # Fedora/RHEL

Open a new shell (or source ~/.bashrc) so the freshly installed tools land on your PATH.

Windows

Use WSL2 (recommended). Several package.json scripts use Unix-shell idioms — inline env vars like BUILD_MODE=oss … and .sh deploy scripts — that do not run under native cmd/PowerShell. WSL2 gives you a real Linux shell where everything works as documented.

wsl --install            # installs Ubuntu; reboot if prompted

Then open the Ubuntu terminal and follow the Linux instructions above. Clone the repo inside the WSL filesystem (e.g. ~/code/…, not /mnt/c/…) for usable file-watch and build performance.

Native Windows (advanced, unsupported)

winget install OpenJS.NodeJS.LTS GoLang.Go Git.Git
powershell -c "irm bun.sh/install.ps1 | iex"

You will still need to work around the Unix-style scripts (e.g. run the editor, AI server, and MP sidecar separately and set BUILD_MODE via $env:BUILD_MODE). WSL2 is strongly preferred.

Verify

bun --version     # 1.0+
go version        # go1.21+
node --version    # v20+

If all three print a version, you're ready for Quick start.

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.
Scheduler & editor settings — frame scheduler architecture, quality presets, performance controls, and profiling tools.
Stem Script — the editor DSL, command-contract boundary, Script Tool mode, and .stemscript game imports.
Built-in behaviors — the behavior model, the full catalog, and how to attach or author one.
Lambdas (ECS layer) — batched, dependency-scheduled systems over many objects, with examples.
Import packs — curated reusable script modules (noise, prng, uikit-dual-mode) and the @import workflow.
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.

Existing games in Stem Script format live in Stem-Studio/Games-StemScript. 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).

WebGPU support is required. We do not support WebGL

Team

_papiguy	_mvromanov	_fayd404	_ikerr
CTO & Venture Lead	Head of Engineering	Head of Product	Platform & Physics
_querielo	_{AndreiRudenko}	_gajendra906	_nafeezable
Three.js Wizard	Games	QA	Community
_JNicoSD	_Jan	_Anand
Games	Games	Head of SRE