Move FX to different position in chain.
AI agents use fx_move 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.
This tool modifies the arrangement of audio effects within a mixing chain, which is a reversible data change. The effects chain configuration is altered but no data is deleted and no external operations are triggered. The impact is confined to the project state and can be undone. While it affects audio output, it is not destructive (effects remain, just reordered) and not Execute (no arbitrary code execution).
From the tool's definition Tool name 'fx_move' and description 'Move FX to different position in chain' indicate reordering/modifying the effects chain state in REAPER.
Documented attack patterns abuse exactly the kind of access fx_move 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_move:
{
"version": "1",
"default": "deny",
"tools": {
"fx_move": {
"limits": [
{
"counter": "fx_move_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}fx_move 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.
Free to start. No card required.
Move FX to different position in chain. 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 fx_move: 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_move 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 fx_move 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_move. 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_move 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.
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