Slack MCP server and Dome

1. 01

   Add the Slack MCP server

   Turn on MCP for your Slack app and give it the user token scopes your agents need. Credentials are per user, through OAuth.

   $ dome tools add --name slack \
     --url https://mcp.slack.com/mcp \
     --auth-method oauth --credential-type per-user \
     --oauth-client-origin manual \
     --oauth-client-id "$SLACK_CLIENT_ID" \
     --oauth-client-secret "$SLACK_CLIENT_SECRET" \
     --oauth-authorize-url https://slack.com/oauth/v2_user/authorize \
     --oauth-token-url https://slack.com/api/oauth.v2.user.access \
     --oauth-token-endpoint-auth client_secret_post \
     --oauth-default-scope search:read.public \
     --oauth-default-scope channels:history \
     --oauth-default-scope chat:write \
     --gateway ops-gateway

2. 02

   Sync the catalog

   Sync spends your own Slack credential, so authorize the app first. Until then it fails and agents get “tool not available in this gateway”.

   $ dome tools catalog sync slack

3. 03

   Apply the rules

   Scope them to one agent while you try them. Simulate before you deploy.

   $ dome rules apply slack-args.cedar \
     --agent escalation-bot --name slack-per-channel

Commands and rules tested against a Dome workspace on October 1, 2026. For anything about Slack itself, see Slack's documentation.

permit (principal, action == Dome::Action::"mcp:call", resource is Dome::MCPTool)
when { resource.connection_name == "slack" };
 
forbid (principal, action == Dome::Action::"mcp:call", resource is Dome::MCPTool)
when {
  resource.connection_name == "slack" &&
  ["slack_send_message", "slack_schedule_message"].contains(resource.tool_name) &&
  resource has arguments && resource.arguments has channel_id &&
  resource.arguments.channel_id != "C04ESCALATE"
};