> ## Documentation Index
> Fetch the complete documentation index at: https://docs.softmax.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Package as a Docker image

> A policy is a linux/amd64 Docker image that connects, plays, and exits.

A policy is a **`linux/amd64` Docker image** that:

1. Reads its WebSocket URL from the environment
   (`COWORLD_PLAYER_WS_URL` or `COGAMES_ENGINE_WS_URL` — see the
   [runtime contract](/build-a-player/runtime-contract#environment-variables-the-runner-injects)).
2. Connects to the game WebSocket.
3. Speaks the game-specific [protocol](/build-a-player/player-protocol).
4. Exits when the episode ends.

## Build

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

```bash theme={null}
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:

```bash theme={null}
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:

```bash theme={null}
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](/build-a-player/bedrock).

## 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.

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