AI agents invoke stop to trigger actions in Reaper. 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.
This tool executes a command in an external application (REAPER DAW) to stop playback. While the operation itself is benign and easily reversible (playback can be restarted), it falls under Execute rather than Write because it runs a control command on an external system rather than creating or modifying persistent data.
From the tool's definition Tool name 'stop' with description 'Stop playback in REAPER' indicates a command that triggers an external operation (stopping audio playback in the REAPER DAW application).
Documented attack patterns abuse exactly the kind of access stop gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Reaper, and nothing reaches the server without passing your rules. This is the rule we recommend for stop:
{
"version": "1",
"default": "deny",
"tools": {
"stop": {
"limits": [
{
"counter": "stop_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}stop 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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Stop playback in REAPER. It is categorised as a Execute tool in the Reaper 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 stop: 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. Nothing to install.
stop 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 stop 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 stop. 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.
stop is provided by the Reaper MCP server (twelvetake-studios/reaper-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Reaper, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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