Set FX parameter by name (fuzzy match).
AI agents use fx_set_param_by_name 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 effect parameters in an audio production context. While parameter changes are reversible (can be undone), they alter the active state of the REAPER project. This is a Write operation rather than Execute because it modifies specific named parameters rather than executing arbitrary code or commands.
From the tool's definition Tool name 'fx_set_param_by_name' and description 'Set FX parameter by name' indicate a modification operation. The verb 'Set' explicitly modifies audio effect parameters in REAPER, which are reversible changes to the mixing/mastering state.
Documented attack patterns abuse exactly the kind of access fx_set_param_by_name 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_set_param_by_name:
{
"version": "1",
"default": "deny",
"tools": {
"fx_set_param_by_name": {
"limits": [
{
"counter": "fx_set_param_by_name_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}fx_set_param_by_name 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.
Set FX parameter by name (fuzzy match). 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_set_param_by_name: 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_set_param_by_name 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_set_param_by_name 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_set_param_by_name. 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_set_param_by_name 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.