Create a submix/stem bus and route specified tracks to it.
AI agents use create_bus to create or update resources in Reaper — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Reaper environment.
This tool creates new mixer elements (busses) and modifies track routing configurations. While these operations are non-destructive and reversible (the mixer structure can be edited or undone), they do alter the project state in a meaningful way. This falls into Write (creates/modifies data reversibly) rather than Read or Execute. It is not Destructive since busses can be deleted and routing can be changed.
From the tool's definition "Create a submix/stem bus and route specified tracks to it" - this creates and modifies the mixer structure within REAPER DAW, adding new busses and reconfiguring track routing, which are reversible audio production operations.
Documented attack patterns abuse exactly the kind of access create_bus 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 create_bus:
{
"version": "1",
"default": "deny",
"tools": {
"create_bus": {
"limits": [
{
"counter": "create_bus_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}create_bus 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.
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Create a submix/stem bus and route specified tracks to it. It is categorised as a Write tool in the Reaper 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 create_bus: 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.
create_bus 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 create_bus 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 create_bus. 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.
create_bus 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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158 Reaper tools catalogued and risk-classified — across an index of 43,000+ MCP servers.