Package as a Docker image

A policy is a linux/amd64 Docker image that:

Reads its WebSocket URL from the environment (COWORLD_PLAYER_WS_URL or COGAMES_ENGINE_WS_URL — see the runtime contract).
Connects to the game WebSocket.
Speaks the game-specific protocol.
Exits when the episode ends.

Build

Always build for linux/amd64, even on an ARM machine:

docker buildx build --platform=linux/amd64 --load -t my-player:latest .

Use a slim Python base, and make your package importable so the runner can start it with a python -m ... entrypoint.

The `--run` argv

The uploaded policy version must have a non-null run attribute — the argv the container runs. A missing or wrong run makes every episode time out and score a loss, regardless of how good your strategy is. Each argv token needs its own --run flag at upload time:

uv run coworld upload-policy my-player:latest --name my-player \
  --run python --run -m --run my_player.module

Use --run repeatedly whenever the default image command is not the player entrypoint. After uploading, verify the run attribute is non-null on the new version.

Secrets — never bake them in

Do not bake secrets into images or public manifests. Provide them at upload time:

uv run coworld upload-policy my-player:latest --name my-player \
  --run python --run -m --run my_player.module \
  --secret-env API_KEY=...

Secrets are stored in AWS Secrets Manager and injected only into that policy version’s player pod. For Bedrock, prefer --use-bedrock (no key needed) — see Bedrock contract.

Best-effort artifact upload

If the runner sets COWORLD_PLAYER_ARTIFACT_UPLOAD_URL, you may upload one .zip per slot (≤200 MB). Handle both the file:// (local) and http(s):// presigned-PUT (hosted) schemes, and never let an upload failure crash the episode.

Sources: adapted from Metta-AI/players docs/coworld-player-packaging.md and Metta-AI/optimizer-agent skills/seed-a-new-policy/SKILL.md.

​Build

​The --run argv

​Secrets — never bake them in

​Best-effort artifact upload

Build

The `--run` argv

Secrets — never bake them in

Best-effort artifact upload