LobbyLab for coding agents

The lobbylab npm package is not published yet, so the npx -y lobbylab commands on this page do not work today. Everything else here is current. Request an alpha key at https://lobbylab.gg/developers.

LobbyLab is a hosted multiplayer backend. Your game keeps its own UI, engine and domain; players join LobbyLab rooms over WebSockets through @lobbylab/client, and LobbyLab keeps the rooms, invite codes, matchmaking and shared game state. Game rules that run on LobbyLab's servers come later. Request an alpha key at https://lobbylab.gg/developers.

Status: alpha. There are no public keys yet, and @lobbylab/client and @lobbylab/node are not on npm yet; both arrive with the alpha. What works today: the lobbylab package's docs and mcp commands, and lobbylab.gg, where people describe a game, LobbyLab builds it, and friends play it on phone or web.

Install the MCP server

It runs locally over stdio, needs no key and makes no network calls. Tools: lobbylab_docs (read these docs) and lobbylab_multiplayer_quickstart (the honest starting point for a stack). Both are read-only.

Claude Code:

claude mcp add lobbylab -- npx -y lobbylab mcp

Codex:

codex mcp add lobbylab -- npx -y lobbylab mcp

Cursor (.cursor/mcp.json) and most other MCP clients:

{ "mcpServers": { "lobbylab": { "command": "npx", "args": ["-y", "lobbylab", "mcp"] } } }

VS Code (.vscode/mcp.json):

{ "servers": { "lobbylab": { "type": "stdio", "command": "npx", "args": ["-y", "lobbylab", "mcp"] } } }

On native Windows, if a client cannot start npx, run it through cmd: command cmd, arguments /c npx -y lobbylab mcp.

Without MCP, the same text is one command away: npx -y lobbylab docs.

Rules for agents during the alpha

• Do not install @lobbylab/client or @lobbylab/node, and do not write code that imports them, until the person has an alpha key and the packages are on npm.
• Do not invent keys, endpoints, package versions or features. If the person needs something the alpha does not have yet, say so plainly.
• Keys, once the person has them: the publishable key goes in LOBBYLAB_PUBLISHABLE_KEY in .env (safe in the browser). The secret key (llsk_...) goes only in .env.local for a backend: never in client code, never printed into chat, logs or commits.
• Test with two players by opening two browser tabs; each tab is its own player.
• If the person only wants to play a game with friends and not build one, lobbylab.gg builds and hosts it for them today.

AGENTS.md section for a project that uses LobbyLab

## Multiplayer (LobbyLab)
This project uses LobbyLab for online multiplayer. Do not write a WebSocket or socket.io server.
- Status: alpha. `@lobbylab/client` is not on npm yet. Add it only once the person has an alpha key
  (request one at https://lobbylab.gg/developers) and the package is published.
- Client: `@lobbylab/client`. The publishable key is LOBBYLAB_PUBLISHABLE_KEY in .env (safe in the browser).
- Never put the secret key (llsk_...) in client code. It lives in .env.local for your backend only.
- Docs for agents: `npx -y lobbylab docs`, or the MCP server `npx -y lobbylab mcp`.
- Test with two players: open two browser tabs; each tab is its own player.

A prompt to copy

Make this game online multiplayer with LobbyLab. First run npx -y lobbylab docs and read it. Keep my UI and engine. Tell me what works today during the alpha and what I need to get started, then use @lobbylab/client for rooms, invite codes and shared state once I have an alpha key. Test with two browser tabs and give me the invite link.

Coming with the alpha and after

• @lobbylab/client and @lobbylab/node on npm.
• npx -y lobbylab@1 init: a sandbox project with no account; the keys are written to .env and .env.local, never printed.
• MCP tools to create projects and rooms, read status and usage, and add test players to a room.
• A Claude Code plugin with a LobbyLab skill and this MCP server, and AGENTS.md in every LobbyLab template.