AI agents use add_fx to create or update resources in Reaper Reapy — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Reaper Reapy environment.
Adding FX (audio effects) to REAPER tracks modifies the project state reversibly—effects can be removed or adjusted later. This is a Write operation rather than Execute because it adds a discrete component rather than executing arbitrary code. Severity is medium because misuse could alter a user's audio project, but changes are reversible.
From the tool's definition Tool name 'add_fx' indicates adding effects to a REAPER DAW project; sibling tools include 'create_track', 'create_midi_item', and other Write operations typical of a DAW control interface. Description is empty, reducing confidence.
Documented attack patterns abuse exactly the kind of access add_fx gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Reaper Reapy, and nothing reaches the server without passing your rules. This is the rule we recommend for add_fx:
{
"version": "1",
"default": "deny",
"tools": {
"add_fx": {
"limits": [
{
"counter": "add_fx_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}add_fx 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. It is categorised as a Write tool in the Reaper Reapy MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Reaper Reapy MCP server in PolicyLayer and add a rule for add_fx: 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 Reaper Reapy. Nothing to install.
add_fx 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 add_fx 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 add_fx. 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.
add_fx is provided by the Reaper Reapy MCP server (wegitor/reaper-reapy-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 47 Reaper Reapy tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
47 Reaper Reapy tools catalogued and risk-classified — across an index of 42,500+ MCP servers.