open_midi_port · Midi MCP: Risk & Policy

WHAT IT DOES

What open_midi_port does on Midi

AI agents invoke open_midi_port to trigger actions in Midi. 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 open_midi_port needs a policy

Opening a MIDI port establishes an external connection/interface to hardware devices (synths, drum machines). This is an operational action that triggers an external system connection rather than simply reading data or writing a record. Misuse could result in unintended MIDI device control or conflicts, warranting medium severity.

From the tool's definition Open a MIDI output port by name

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

open_midi_port Rate-limited

open_midi_port 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": {
    "open_midi_port": {
      "limits": [
        {
          "counter": "open_midi_port_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 Midi, so you can run agents against it safely.

FAQ

Questions about open_midi_port

What does the open_midi_port tool do? +

Open a MIDI output port by name. Use list_midi_ports to see available ports. It is categorised as a Execute tool in the Midi MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on open_midi_port? +

Register the Midi MCP server in PolicyLayer and add a rule for open_midi_port: 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 Midi. Nothing to install.

What risk level is open_midi_port? +

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

Can I rate-limit open_midi_port? +

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

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

open_midi_port is provided by the Midi MCP server (pnilan/midi-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.