send_message · Claude Code MCP Controller MCP: Risk & Policy

WHAT IT DOES

What send_message does on Claude Code MCP Controller

AI agents invoke send_message to trigger actions in Claude Code MCP Controller. 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 a Claude Code session causes that session to interpret and act on the message, which may result in code execution, file system changes, shell commands, or other operations depending on the message content. The blast radius is high because the downstream effects are unbounded and depend on what the session does in response.

From the tool's definition Send a message to a Claude-Code session — triggers arbitrary natural language commands in an active Claude Code session, which can execute code, run shell commands, modify files, etc.

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 Claude Code MCP Controller, so you can run agents against it safely.

FAQ

Questions about send_message

What does the send_message tool do? +

Send a message to a Claude-Code session. It is categorised as a Execute tool in the Claude Code MCP Controller 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 Claude Code MCP Controller 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 Claude Code MCP Controller. 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 Claude Code MCP Controller MCP server (mostafa-drz/claude-code-mcp-controller). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.