Toggle metronome.
AI agents invoke transport_toggle_metronome to trigger actions in ReaperMCP. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.
Toggling the metronome is an action that changes the state of an external application (REAPER). It's not purely reading data, nor writing/creating persistent data, nor destructive. It executes a state-change command in the DAW environment. Blast radius is low as it only affects metronome audibility during playback.
From the tool's definition Toggle metronome — triggers an external operation in REAPER that changes the state of the metronome playback setting
Documented attack patterns abuse exactly the kind of access transport_toggle_metronome 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 transport_toggle_metronome:
{
"version": "1",
"default": "deny",
"tools": {
"transport_toggle_metronome": {
"limits": [
{
"counter": "transport_toggle_metronome_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}transport_toggle_metronome stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
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Toggle metronome. It is categorised as a Execute tool in the ReaperMCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Reaper MCP server in PolicyLayer and add a rule for transport_toggle_metronome: 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.
transport_toggle_metronome is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the transport_toggle_metronome 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 transport_toggle_metronome. 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.
transport_toggle_metronome 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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