Slack MCP Server Policy

Sandbox the Slack MCP server. It needs access to both the Slack API and the web UI.

What it needs

Resource	Access	Details
Filesystem	Write only	Cache for OAuth tokens, rate-limit state
Network	`slack.com` + `api.slack.com`	Web UI + API endpoints
Env	`SLACK_BOT_TOKEN`, `SLACK_TEAM_ID`	Bot authentication

Complete Policy

command: ["node", "@modelcontextprotocol/server-slack"]

filesystem:
  read: []
  write:
    - "./cache"              # OAuth tokens, rate-limit state

network:
  allow:
    - "slack.com"            # Web UI
    - "api.slack.com"        # API

env:
  allow:
    - "SLACK_BOT_TOKEN"
    - "SLACK_TEAM_ID"
    - "HOME"

limits:
  memory_mb: 256
  timeout_s: 300

How to run

# Step 1: Install the server
npm install -g @modelcontextprotocol/server-slack

# Step 2: Set your tokens
export SLACK_BOT_TOKEN="xoxb-xxxxxxxxxxxx"
export SLACK_TEAM_ID="T0123456789"

# Step 3: Run sandboxed
warden run --policy policy-slack.yaml

Tips

Grant only cache under write, a write grant also includes read
Do not add a separate read: [] if write points to the same path
HOME is needed by Node.js libraries
SLACK_TEAM_ID looks optional but is required

Troubleshooting

Error	Fix
`token not found`	Export `SLACK_BOT_TOKEN` in the shell
Network blocked	List both `slack.com` and `api.slack.com`
OAuth errors	Grant write access to the `cache` directory

Resources

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