MCP Arcade

GameDay for MCP servers. The house keeps the tape.

You point Arcade at a server. It runs four named experiments. The oracle is the JSON-RPC wire: which tools/call went out, with which arguments, and whether the sandbox changed. It does not score a regex on a tool description, a flourish in a TUI, or a model essay.

A full bar is not a safety certificate. It is “these experiments did not catch a lie this time.”

The tape that comes out can be played as Ghost on the Menu, a short arcade shooter in the sister repo. The instrument scores the wire. The game never does.

The four experiments

That is the whole catalog.

The agent on the other end is a policy, not a judge: naive follows “also call X” whispers, task-only runs the named tool and stops, ollama:<model> is a local model that sees the menu and emits calls. naive and task-only are the controls.

Install

pip install mcp-arcade

Python 3.11 or later. From a clone: pip install -e ".[dev]".

Run a bout

# Lab fixture. No --allow-live needed. naive will follow the whisper.
mcp-arcade bout --target fixture --agent naive --no-prompt -o receipt.json

# Same lab, policy that refuses whispered errands.
mcp-arcade bout --target fixture --agent task-only --no-prompt

# Your stdio server. Fail-closed: opt in, and name a benign task.
mcp-arcade bout --target stdio \
  --cmd python --cmd -m --cmd your_server \
  --task your_read_only_tool \
  --allow-live --no-prompt

mcp-arcade atoms lists the catalog. Leave off --no-prompt in a real terminal: Arcade asks what you think the wire will show before it posts the score.

Docker is the sandbox for a real container. The fixture image needs no --allow-live; your image always does. See the handbook for flags, framing, the local-model seat, and what a green bar is not.

Keep the tape

mcp-arcade receipt receipt.json --timeline    # one row per wire event, no score
mcp-arcade tape receipt.json -o tape.json     # the cabinet's input

The timeline is the diagnostic: every tools/call, every reply, every notification. Scores stay off it until you ask. The tape file is what Ghost on the Menu reads. Arcade never writes a game score onto it.

More

• Handbook — install, a first bout, the CLI, how scoring works
• Changelog — what shipped in each wave
• SECURITY.md — default is the lab fixture; live servers need --allow-live; no telemetry
• Live fire — a real SDK server, the controls, and the limits of 0.x

Do not point --allow-live at a production server that can reach real secrets. Read a live receipt before you share it.

MIT. See LICENSE.