AI agents use tempo_add_marker to create or update resources in ReaperMCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your ReaperMCP environment.
Tempo markers in REAPER are reversible modifications to project state—they can be edited or deleted. This is a Write operation rather than Execute because it modifies structured data (a marker) rather than triggering arbitrary external behavior. Severity is medium because incorrect marker placement could disrupt workflow, but changes are easily undone. Confidence is lowered due to the empty description.
From the tool's definition Tool named 'tempo_add_marker' with no description; sibling tools like 'create_chord_progression' and 'create_drum_pattern' confirm this server performs music production modifications. The 'add' verb suggests creating/modifying data (markers in a DAW timeline).
Documented attack patterns abuse exactly the kind of access tempo_add_marker 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 tempo_add_marker:
{
"version": "1",
"default": "deny",
"tools": {
"tempo_add_marker": {
"limits": [
{
"counter": "tempo_add_marker_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}tempo_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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tempo_add_marker. It is categorised as a Write tool in the ReaperMCP 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 tempo_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 ReaperMCP. Nothing to install.
tempo_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 tempo_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 tempo_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.
tempo_add_marker 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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