AI agents use open_project 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.
Opening a project file is a state-modifying operation that changes the active project context in REAPER. While not destructive (the previous project is not deleted), it transitions the application state and could overwrite unsaved work in the current project if the user has not saved. This qualifies as Write rather than Read because it causes reversible side effects on the application state.
From the tool's definition Tool name: 'open_project'. Description: 'Open a REAPER project file.' The action of opening a project file in REAPER (a DAW) will load project state, potentially modify the current working state, and depending on REAPER's behavior, may alter or replace the…
Documented attack patterns abuse exactly the kind of access open_project 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 open_project:
{
"version": "1",
"default": "deny",
"tools": {
"open_project": {
"limits": [
{
"counter": "open_project_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}open_project 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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Open a REAPER project file. 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 open_project: 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.
open_project 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 open_project 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 open_project. 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.
open_project 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.