Set MIDI item boundaries in quarter notes.
AI agents use midi_set_item_extents 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.
The tool modifies MIDI item properties (boundaries/extents) within a REAPER project. This is a Write operation because it creates or modifies data reversibly. The severity is medium because while the change affects musical content and project structure, it is reversible (can be undone/adjusted). It is not Destructive because boundaries can be extended or contracted again, not irreversibly deleted.
From the tool's definition 'Set MIDI item boundaries in quarter notes' - this modifies the temporal extents of MIDI items, a reversible change to project data.
Documented attack patterns abuse exactly the kind of access midi_set_item_extents 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 midi_set_item_extents:
{
"version": "1",
"default": "deny",
"tools": {
"midi_set_item_extents": {
"limits": [
{
"counter": "midi_set_item_extents_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}midi_set_item_extents 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 MIDI item boundaries in quarter notes. 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 midi_set_item_extents: 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.
midi_set_item_extents 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 midi_set_item_extents 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 midi_set_item_extents. 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.
midi_set_item_extents 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.
Free to start. No card required.
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