Find VSTi instrument on track. Returns index + params, or -1 if none.
AI agents call fx_get_instrument to retrieve information from ReaperMCP without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This is a straightforward data retrieval tool that queries the state of a REAPER track to identify an instrument and return its parameters. It has no side effects, does not execute code or commands, does not modify data, and does not perform destructive operations. The read-only nature and minimal blast radius if misused by an AI agent justify the 'Read' category and 'low' severity classification.
From the tool's definition Tool name and description indicate a query operation: 'Find VSTi instrument on track. Returns index + params, or -1 if none.' This retrieves information about an existing instrument without modifying, executing, or deleting anything.
Documented attack patterns abuse exactly the kind of access fx_get_instrument 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 fx_get_instrument:
{
"version": "1",
"default": "deny",
"tools": {
"fx_get_instrument": {}
}
}fx_get_instrument is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Find VSTi instrument on track. Returns index + params, or -1 if none. It is categorised as a Read tool in the ReaperMCP MCP Server, which means it retrieves data without modifying state.
Register the Reaper MCP server in PolicyLayer and add a rule for fx_get_instrument: 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.
fx_get_instrument is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the fx_get_instrument 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 fx_get_instrument. 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.
fx_get_instrument 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.
Free to start. No card required.
138 ReaperMCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.