send_formatted_message · Slack MCP Server MCP: Risk & Policy

WHAT IT DOES

What send_formatted_message does on Slack MCP Server

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

WHY IT NEEDS A POLICY

Why send_formatted_message needs a policy

This tool creates or posts formatted messages to Slack channels, which is a reversible write operation. The message can be edited or deleted later. While it could be misused to spam or send misleading content, the blast radius is limited to message creation without irreversible data loss or financial impact.

From the tool's definition Tool name 'send_formatted_message' indicates message creation/modification in Slack. Server description states 'messaging' and 'Block Kit formatting' capabilities.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

send_formatted_message Rate-limited

send_formatted_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": {
    "send_formatted_message": {
      "limits": [
        {
          "counter": "send_formatted_message_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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Instant setup, no code required.

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

FAQ

Questions about send_formatted_message

What does the send_formatted_message tool do? +

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

How do I enforce a policy on send_formatted_message? +

Register the Slack MCP Server MCP server in PolicyLayer and add a rule for send_formatted_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 Server. Nothing to install.

What risk level is send_formatted_message? +

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

Can I rate-limit send_formatted_message? +

Yes. Add a rate_limit block to the send_formatted_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 send_formatted_message completely? +

Set action: deny in the PolicyLayer policy for send_formatted_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 send_formatted_message? +

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