# shell

Makes packages available in the environment and optionally runs a command. Returns stdout, stderr, exit code, and duration.

Agent View of the PolicyLayer registry record for `shell`. HTML page: https://policylayer.com/tools/io-github-dave-london-cargo/shell

## Facts

- Tool: `shell`
- Server: Cargo (`Dave-London/Pare`) — https://policylayer.com/tools/io-github-dave-london-cargo.md
- Homepage: https://github.com/Dave-London/pare
- Risk category: Execute (High risk)
- Registry record: grade F, identity unverified
- Server rate-limited: no
- Parameters: 0
- Recommended policy verdict: Rate-limited

## Example call (MCP tools/call, JSON-RPC 2.0)

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "shell",
    "arguments": {}
  }
}
```

## Why shell is rated High

The tool explicitly runs commands and returns execution results (stdout, stderr, exit code). This is a general-purpose shell execution primitive with no apparent restrictions on what commands can be run. An AI agent could use this to run any arbitrary command, making it critical severity due to the unlimited blast radius — data exfiltration, system modification, destructive operations, and more are all possible.

From the tool's own definition: "'optionally runs a command' and 'Returns stdout, stderr, exit code, and duration' — this tool executes arbitrary shell commands in the environment"

## Use case

AI agents invoke shell to trigger actions in Cargo. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call: builds kicked off, notifications sent, workflows started.

## Recommended policy (PolicyLayer)

Verdict: **Rate-limited**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches Cargo:

```json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "shell": {
      "limits": [
        {
          "counter": "shell_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}
```

## Other tools on Cargo (201)

- `branch` — Destructive — https://policylayer.com/tools/io-github-dave-london-cargo/branch.md
- `clean` — Destructive — https://policylayer.com/tools/io-github-dave-london-cargo/clean.md
- `pr-close` — Destructive — https://policylayer.com/tools/io-github-dave-london-cargo/pr-close.md
- `remove` — Destructive — https://policylayer.com/tools/io-github-dave-london-cargo/remove.md
- `reset` — Destructive — https://policylayer.com/tools/io-github-dave-london-cargo/reset.md
- `secret-delete` — Destructive — https://policylayer.com/tools/io-github-dave-london-cargo/secret-delete.md
- `tag` — Destructive — https://policylayer.com/tools/io-github-dave-london-cargo/tag.md
- `variable-delete` — Destructive — https://policylayer.com/tools/io-github-dave-london-cargo/variable-delete.md
- `workspace` — Destructive — https://policylayer.com/tools/io-github-dave-london-cargo/workspace.md
- `add` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/add.md
- `add-package` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/add-package.md
- `ansible-galaxy` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/ansible-galaxy.md
- `ansible-playbook` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/ansible-playbook.md
- `api` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/api.md
- `apply` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/apply.md
- `bazel` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/bazel.md
- `biome-check` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/biome-check.md
- `bisect` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/bisect.md
- `black` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/black.md
- `build` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/build.md
- `bundle-exec` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/bundle-exec.md
- `bundle-install` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/bundle-install.md
- `check` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/check.md
- `cherry-pick` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/cherry-pick.md
- `clippy` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/clippy.md
- `cmake` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/cmake.md
- `compose-build` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/compose-build.md
- `compose-down` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/compose-down.md
- `compose-up` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/compose-up.md
- `conda` — Execute — https://policylayer.com/tools/io-github-dave-london-cargo/conda.md
- …and 171 more: https://policylayer.com/tools/io-github-dave-london-cargo.md

## For agents

This record is a snapshot. Live verdicts and the full registry:

- Check every server in your MCP config at once: `npx -y policylayer stack`
- Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md)
- Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events`

---

Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=io-github-dave-london-cargo · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/io-github-dave-london-cargo