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Summer Engine with Local Models

You don’t need an AI subscription to build games in Summer Engine. Any local model that handles tool calling can drive the engine through MCP: add nodes, set properties, search and import assets, run the game, and debug. Engine control and asset search are free; cloud generation (3D models, images, audio) uses credits. This page covers the three setups that actually work in 2026.

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Prerequisites

  • A GPU with 12 GB+ of VRAM (or Apple Silicon with 16 GB+ unified memory). 24 GB is the sweet spot.
  • Node.js: For running the MCP server (Node 18+)
  • Summer Engine: Installed and running with your project open

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Option 1: LM Studio (easiest)

LM Studio is both the model runtime and an MCP host — one app, no terminal. 
npx -y summer-engine@latest setup lm-studio --yes
This writes the summer-engine server into ~/.lmstudio/mcp.json. Then, in LM Studio:
  1. Download a model in the Discover tab (see model picks below).
  2. Toggle the summer-engine MCP server on in the Program tab.
  3. Raise the model’s context length to 32k or higher when loading it. Models load with the context baked into their metadata — often ~4k, which MCP tool schemas overflow silently.
  4. Keep KV-cache quantization off for long agent sessions. On Apple Silicon, prefer the MLX builds.
Every engine call shows a confirmation dialog you can review before it runs.

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Option 2: OpenCode + Ollama (terminal)

The most common pairing in 2026. Ollama serves the model; OpenCode is the agent. 
# 1. Fix the context window FIRST — Ollama defaults to 4k under 24 GB VRAM,
#    which silently breaks MCP tool calling
OLLAMA_CONTEXT_LENGTH=65536 ollama serve

# 2. Pull a model
ollama pull qwen3-coder:30b

# 3. Wire Summer Engine into OpenCode
npx -y summer-engine@latest setup opencode --yes
Then point OpenCode’s provider at Ollama (http://localhost:11434/v1 as an OpenAI-compatible endpoint) and select your model. Run ollama ps to confirm the bigger context hasn’t pushed the model off the GPU. The same Ollama backend works with Kilo Code in VS Code (npx -y summer-engine@latest setup kilo-code --yes) — set the context window to 32k+ in Kilo’s provider settings.

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Option 3: Goose (agent-first)

Goose is an open-source agent that treats MCP servers as extensions.
  1. Run goose configure → Add Extension → Command-line Extension, command: npx -y summer-engine@latest mcp
  2. Run goose configure → Configure Providers → Ollama, host localhost:11434
  3. Pick a model with native tool calling — Goose’s toolshim mode for non-tool-calling models is slower and less reliable.
In Goose Desktop, both live under Settings → Extensions and Settings → Providers.

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Which Model to Run

Tool calling is the hard part for local models. Use Q4_K_M quantization or better — heavier quantization breaks tool calls before it breaks chat.
HardwareModelNotes
12–16 GB VRAMgpt-oss-20bThe tier’s default; supported everywhere
24 GB VRAM (3090/4090)Qwen3-Coder-30B or Gemma 4 27BThe community sweet spot for engine work
8 GB VRAMQwen3.5-4BSmall scenes only; expect retries on long tool chains
Apple Silicon 32 GB+Same picks, MLX buildsMLX is faster for long agentic loops

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Troubleshooting

  • The model never calls tools, or hallucinates them: context window too small. MCP tool schemas plus the system prompt overflow a 4k–8k window instantly. Set 32k minimum, 64k recommended.
  • Tool calls come out malformed: quantization too aggressive (use Q4_K_M+), or the model is too small (7B is the practical floor, 14B+ for multi-server setups).
  • Cline users: Cline’s “compact prompt” option for local models disables MCP entirely. Keep the full system prompt on.
  • Slow first response: keep only a couple of MCP servers enabled so tool schemas leave room for actual work.

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What’s Free and What Isn’t

Engine control (scenes, nodes, scripts, play, debug)Free
Asset library search (25k+ assets)Free, rate-limited
Cloud generation (3D, image, audio, video)Credits
Sign in once with npx summer-engine login — the account is the rate-limit key, not a paywall.