send_message · Shannon MCP: Risk & Policy

WHAT IT DOES

What send_message does on Shannon MCP

AI agents invoke send_message to trigger actions in Shannon MCP. 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.

WHY IT NEEDS A POLICY

Why send_message needs a policy

Sending a message to an active Claude Code CLI session drives the agent to perform actions (run code, execute shell commands, file operations, etc.) whose effects depend entirely on the message content. This is an indirect execution primitive — the blast radius is high because an attacker or misbehaving agent could craft messages that cause the session to perform destructive or sensitive operations.

From the tool's definition "Send a message to an active session" — dispatches input to a running Claude Code CLI session, triggering execution of whatever operation or command the message encodes.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

send_message Rate-limited

send_message stays usable, but rate-capped — a runaway agent can't fire it dozens of times 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_message": {
      "limits": [
        {
          "counter": "send_message_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

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

FAQ

Questions about send_message

What does the send_message tool do? +

Send a message to an active session. It is categorised as a Execute tool in the Shannon MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on send_message? +

Register the Shannon MCP server in PolicyLayer and add a rule for 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 Shannon MCP. Nothing to install.

What risk level is send_message? +

send_message is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit send_message? +

Yes. Add a rate_limit block to the 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 send_message completely? +

Set action: deny in the PolicyLayer policy for 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 send_message? +

send_message is provided by the Shannon MCP server (krzemienski/shannon-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.