Set the source channels for a send.
AI agents use set_send_source_channels 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.
The tool modifies DAW mixer state (send routing) in a way that can be undone or adjusted, making it a Write operation rather than Read (it changes state), Execute (it doesn't run arbitrary code), Destructive (changes are reversible), or Financial (no money involved).
From the tool's definition set_send_source_channels modifies audio routing configuration by setting which source channels are routed to a send, which changes the mixer state in a reversible manner.
Documented attack patterns abuse exactly the kind of access set_send_source_channels 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 set_send_source_channels:
{
"version": "1",
"default": "deny",
"tools": {
"set_send_source_channels": {
"limits": [
{
"counter": "set_send_source_channels_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}set_send_source_channels 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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Set the source channels for a send. 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 set_send_source_channels: 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.
set_send_source_channels 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 set_send_source_channels 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 set_send_source_channels. 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.
set_send_source_channels 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.
Free to start. No card required.
158 Reaper tools catalogued and risk-classified — across an index of 43,000+ MCP servers.