send_sysex · Midi MCP: Risk & Policy

WHAT IT DOES

What send_sysex does on Midi

AI agents invoke send_sysex 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 send_sysex needs a policy

SysEx (System Exclusive) messages are arbitrary binary commands sent directly to MIDI hardware. They can reconfigure synthesizer parameters, overwrite firmware, reset devices, or alter patch memory in ways that may be irreversible depending on the target device.

From the tool's definition Send a MIDI System Exclusive message

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

send_sysex Rate-limited

send_sysex 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_sysex": {
      "limits": [
        {
          "counter": "send_sysex_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 send_sysex

What does the send_sysex tool do? +

Send a MIDI System Exclusive message. 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 send_sysex? +

Register the Midi MCP server in PolicyLayer and add a rule for send_sysex: 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 send_sysex? +

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

Can I rate-limit send_sysex? +

Yes. Add a rate_limit block to the send_sysex 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_sysex completely? +

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

send_sysex 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.