Set the length of a media item.
AI agents use set_item_length 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 modifies the length attribute of media items, which is a reversible change to project state. It does not delete data (Destructive), execute arbitrary code (Execute), or involve financial transactions. However, it does alter project structure in a way that could affect audio timing and alignment, and if misused could corrupt layered compositions.
From the tool's definition Tool named 'set_item_length' with description 'Set the length of a media item' – this modifies existing media item properties in the DAW project.
Documented attack patterns abuse exactly the kind of access set_item_length 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_item_length:
{
"version": "1",
"default": "deny",
"tools": {
"set_item_length": {
"limits": [
{
"counter": "set_item_length_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}set_item_length 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 length of a media item. 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_item_length: 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_item_length 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_item_length 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_item_length. 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_item_length 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.