slack_send_message · Slack MCP: Risk & Policy

WHAT IT DOES

What slack_send_message does on Slack MCP

AI agents use slack_send_message to create or update resources in Slack MCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Slack MCP environment.

WHY IT NEEDS A POLICY

Why slack_send_message needs a policy

This tool creates new messages in Slack channels or direct messages, which modifies workspace state reversibly (messages can be edited/deleted). It is Write category rather than Execute because it directly modifies communication data rather than triggering external actions.

From the tool's definition Tool name 'slack_send_message' and description 'Send a message to a Slack channel or user' indicate creation of new message content in Slack.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

slack_send_message Rate-limited

slack_send_message stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "slack_send_message": {
      "limits": [
        {
          "counter": "slack_send_message_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Slack MCP, so you can run agents against it safely.

FAQ

Questions about slack_send_message

What does the slack_send_message tool do? +

Send a message to a Slack channel or user. It is categorised as a Write tool in the Slack MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on slack_send_message? +

Register the Slack MCP server in PolicyLayer and add a rule for slack_send_message: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Slack MCP. Nothing to install.

What risk level is slack_send_message? +

slack_send_message is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit slack_send_message? +

Yes. Add a rate_limit block to the slack_send_message rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block slack_send_message completely? +

Set action: deny in the PolicyLayer policy for slack_send_message. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides slack_send_message? +

slack_send_message is provided by the Slack MCP server (neilkuo-opennet/slack-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.