Select/deselect all notes in item.
AI agents use midi_select_notes to create or update resources in ReaperMCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your ReaperMCP environment.
Selecting/deselecting notes modifies the selection state within a MIDI item in REAPER. This is a reversible state change (Write), not a destructive operation. The blast radius is low since it only affects note selection, which can be easily undone.
From the tool's definition Select/deselect all notes in item
Documented attack patterns abuse exactly the kind of access midi_select_notes gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and ReaperMCP, and nothing reaches the server without passing your rules. This is the rule we recommend for midi_select_notes:
{
"version": "1",
"default": "deny",
"tools": {
"midi_select_notes": {
"limits": [
{
"counter": "midi_select_notes_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}midi_select_notes 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.
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Select/deselect all notes in item. It is categorised as a Write tool in the ReaperMCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Reaper MCP server in PolicyLayer and add a rule for midi_select_notes: 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 ReaperMCP. Nothing to install.
midi_select_notes is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the midi_select_notes 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 midi_select_notes. 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.
midi_select_notes is provided by the Reaper MCP server (xdarkzx/reaper-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from ReaperMCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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