AI agents call fx_list_installed 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.
The tool appears to enumerate or retrieve information about installed effects/plugins in REAPER without modifying, executing, or deleting anything. This is consistent with Read category tools that query system state. Low severity because listing installed plugins poses minimal risk—it only exposes information about the audio production environment.
From the tool's definition Tool name 'fx_list_installed' indicates a list/query operation retrieving installed effects. The verb 'list' is a classic Read pattern. No description provided, but the naming convention strongly suggests data retrieval with no side effects.
Documented attack patterns abuse exactly the kind of access fx_list_installed 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_list_installed:
{
"version": "1",
"default": "deny",
"tools": {
"fx_list_installed": {}
}
}fx_list_installed is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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fx_list_installed. 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_list_installed: 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_list_installed 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_list_installed 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_list_installed. 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_list_installed 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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138 ReaperMCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.