send_message_to_session · Tmux MCP Server MCP: Risk & Policy

WHAT IT DOES

What send_message_to_session does on Tmux MCP Server

AI agents invoke send_message_to_session to trigger actions in Tmux MCP Server. 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_to_session needs a policy

Sending a message to a tmux session effectively executes commands or input in that session. This can trigger arbitrary shell commands, scripts, or process interactions depending on what is sent. The blast radius is high because an AI agent could send malicious or unintended commands to active terminal sessions, affecting running processes, files, or system state.

From the tool's definition Send a message to a specific tmux session

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

send_message_to_session Rate-limited

send_message_to_session 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_to_session": {
      "limits": [
        {
          "counter": "send_message_to_session_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 Tmux MCP Server, so you can run agents against it safely.

FAQ

Questions about send_message_to_session

What does the send_message_to_session tool do? +

Send a message to a specific tmux session. It is categorised as a Execute tool in the Tmux MCP Server 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_to_session? +

Register the Tmux MCP Server MCP server in PolicyLayer and add a rule for send_message_to_session: 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 Tmux MCP Server. Nothing to install.

What risk level is send_message_to_session? +

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

Can I rate-limit send_message_to_session? +

Yes. Add a rate_limit block to the send_message_to_session 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_to_session completely? +

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

send_message_to_session is provided by the Tmux MCP Server MCP server (rinadelph/tmux-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.