AI agents use add_marker 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.
Adding a marker is a write operation that creates new data (a marker) in the REAPER project. While reversible (markers can be deleted), it modifies project state. This is not a read operation (it doesn't merely retrieve data), not destructive (markers can be removed), and not execute/financial.
From the tool's definition Tool name is 'add_marker' and description states 'Add a marker at a position.' This creates a new marker object in the DAW project, which is a reversible modification to the project data.
Documented attack patterns abuse exactly the kind of access add_marker 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 add_marker:
{
"version": "1",
"default": "deny",
"tools": {
"add_marker": {
"limits": [
{
"counter": "add_marker_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}add_marker 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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Add a marker at a position. 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 add_marker: 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.
add_marker 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_marker 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_marker. 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_marker 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.