AI agents invoke send_note_on to trigger actions in MCP MIDI 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.
This tool executes an external operation (sending a MIDI Note On message via a virtual MIDI port to downstream software). It does not read data, modify stored data, delete anything, or involve finances. It is an outbound trigger/signal, making Execute the appropriate category. Severity is low as the blast radius is limited to MIDI signal output with no meaningful system or data impact.
From the tool's definition 'Sends a MIDI Note On message' — triggers an external MIDI operation by transmitting a control signal to connected MIDI software
Documented attack patterns abuse exactly the kind of access send_note_on gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and MCP MIDI Server, and nothing reaches the server without passing your rules. This is the rule we recommend for send_note_on:
{
"version": "1",
"default": "deny",
"tools": {
"send_note_on": {
"limits": [
{
"counter": "send_note_on_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}send_note_on 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.
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Sends a MIDI Note On message. It is categorised as a Execute tool in the MCP MIDI Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the MCP MIDI Server MCP server in PolicyLayer and add a rule for send_note_on: 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 MCP MIDI Server. Nothing to install.
send_note_on is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the send_note_on 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.
Set action: deny in the PolicyLayer policy for send_note_on. 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.
send_note_on is provided by the MCP MIDI Server MCP server (sandst1/mcp-server-midi). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from MCP MIDI Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
4 MCP MIDI Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.