summer

Summer Engine: the AI game engine

Build real 2D and 3D games through conversation. No coding required. Export to Steam, desktop, mobile, and web. Built on the Godot team's work, customized and honed so AI agents and humans can collaborate on great games.

Summer is the MIT open-source agent layer that connects your AI coding agent to Summer Engine. It is the Summer CLI, the Summer MCP server, and the Summer agent skills, hooks, and plugin manifests, all in one package. First-class setup works in Claude Code, Cursor, Codex, Windsurf, Cline, Roo Code, Gemini CLI, GitHub Copilot CLI, GitHub Copilot in VS Code, and OpenCode. Factory Droid uses the plugin marketplace path.

• Source: github.com/SummerEngine/summer-engine-agent
• CLI setup: www.summerengine.com/cli
• MCP setup: www.summerengine.com/mcp
• Docs: docs.summerengine.com

It just works. Open your agent, say "let's make an FPS in Summer Engine," and it does.

---

Summer CLI, Summer MCP, and the Summer agent

Three names, one npm package (summer-engine):

• Summer CLI (npx -y summer-engine@latest): installs the engine, signs you in, scaffolds and runs projects, and writes your agent's config. See www.summerengine.com/cli.
• Summer MCP: the local MCP server that gives your agent 44 engine tools to build, run, and debug a real game. See www.summerengine.com/mcp.
• Summer agent layer: the game-dev skills, hooks, and plugin manifests that give your AI agent judgment, not just a chat box.

All MIT, all free to use. One paste sets up all three.

---

Get started: one prompt

Open your AI agent (Claude Code, Cursor, Codex, Copilot, Windsurf, etc.) and paste:

Install Summer Engine and let's make a game. Read github.com/SummerEngine/summer-engine-agent, check what I already have installed, install whatever is missing, log me in, and scaffold a starter project so we can start building.

That's it. The agent reads this README, detects what's already on your machine, and runs only what's missing via Bash. No /plugin slash commands. No manual installs. One paste.

The first run will:

1. Install the summer-engine npm package (~3 MB) if it's not on PATH.
2. Install Summer's game-dev skills into ~/.claude/skills/ (or your agent's user-skill directory) so the agent loads them next session.
3. Download the Summer Engine app (~1 GB, including the engine binary, Git, and other runtime tools so users without them aren't blocked) if it's not installed.
4. Open your browser for one-click sign-in.
5. Scaffold a starter project and open the engine.

At that point the agent has the skills, the MCP server, and your engine running. Ask it to build something.

---

AGENTS READING THIS: install playbook

You are an AI coding agent. The user told you to install Summer Engine. Run this playbook via your shell: Bash on macOS/Linux or PowerShell on Windows. npx -y is shell-agnostic and works identically in both. Detection first, then only install what's missing.

Step -1: Verify Node.js is on PATH

node --version

If this command does not print Node.js 18 or newer, stop. Tell the user: "Summer needs Node.js 18+. Install from https://nodejs.org and re-run the prompt." Do NOT try to install Node yourself.

Step 0: Pre-detection (no commits to disk, just check state)

npx -y summer-engine@latest doctor --json

The first invocation downloads the npm package transparently to npx's cache (~3 MB, ~5 sec). Subsequent calls are fast. The -y flag auto-confirms npx's "ok to install summer-engine?" prompt so the call doesn't hang in a non-interactive shell.

Read the JSON output. If top-level ok is true, everything is installed and you can skip straight to Step 5. Otherwise use the checks array to run only the remediation steps that need attention.

The relevant check ids are node-version, cli-version, cli-version-current, skills-version-stale, login, engine-install, local-api, project-memory, and mcp-server. For any check that is not ok, run the action in the table below, then re-run doctor.