Add FX plugin to track. Prefer setup_fx_chain for batch operations.
AI agents use fx_add 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 creates a new effect plugin on a track, which is a non-destructive modification that can be undone. It modifies the track configuration but does not execute arbitrary code, delete data, or move money. The reversible nature of adding/removing plugins classifies it as Write rather than Execute.
From the tool's definition Tool name is 'fx_add' and description states 'Add FX plugin to track', which creates a new effect plugin instance on an audio track—a reversible modification to the project state.
Documented attack patterns abuse exactly the kind of access fx_add 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_add:
{
"version": "1",
"default": "deny",
"tools": {
"fx_add": {
"limits": [
{
"counter": "fx_add_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}fx_add 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.
Add FX plugin to track. Prefer setup_fx_chain for batch operations. 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_add: 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_add 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_add 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_add. 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_add 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.