msg_send · Agent Messaging MCP: Risk & Policy

WHAT IT DOES

What msg_send does on Agent Messaging

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

WHY IT NEEDS A POLICY

Why msg_send needs a policy

This tool creates new message records in a messaging system and transmits them to another agent. It is reversible (messages can typically be edited or deleted in asynchronous systems), so it qualifies as Write rather than Destructive.

From the tool's definition Tool name 'msg_send' and description 'Send a message to another agent' indicates creation and transmission of data (a message) to another system. Returns 'message_id, timestamp, delivery_status' confirming the message is created and recorded.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

msg_send Rate-limited

msg_send 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": {
    "msg_send": {
      "limits": [
        {
          "counter": "msg_send_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 Agent Messaging, so you can run agents against it safely.

FAQ

Questions about msg_send

What does the msg_send tool do? +

Send a message to another agent. Returns message_id, timestamp, delivery_status. It is categorised as a Write tool in the Agent Messaging MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on msg_send? +

Register the Agent Messaging MCP server in PolicyLayer and add a rule for msg_send: 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 Agent Messaging. Nothing to install.

What risk level is msg_send? +

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

Can I rate-limit msg_send? +

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

Set action: deny in the PolicyLayer policy for msg_send. 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 msg_send? +

msg_send is provided by the Agent Messaging MCP server (rumblingb/agent-messaging-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.