append · Filopastry MCP: Risk & Policy

WHAT IT DOES

What append does on Filopastry

AI agents use append to create or update resources in Filopastry — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Filopastry environment.

WHY IT NEEDS A POLICY

Why append needs a policy

The tool creates or modifies data (the current music pattern) in a reversible manner. It does not execute code or trigger real-time audio operations (those would be Execute), nor does it delete or permanently remove data (Destructive). The modification is reversible because appended code can be edited or undone.

From the tool's definition Tool description states 'Append code to current pattern' — this modifies the existing pattern by adding code to it, which is a reversible write operation.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

append Rate-limited

append 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.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "append": {
      "limits": [
        {
          "counter": "append_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Filopastry, so you can run agents against it safely.

FAQ

Questions about append

What does the append tool do? +

Append code to current pattern. It is categorised as a Write tool in the Filopastry MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on append? +

Register the Filopastry MCP server in PolicyLayer and add a rule for append: 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 Filopastry. Nothing to install.

What risk level is append? +

append is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit append? +

Yes. Add a rate_limit block to the append 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.

How do I block append completely? +

Set action: deny in the PolicyLayer policy for append. 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.

What MCP server provides append? +

append is provided by the Filopastry MCP server (youwenshao/filopastry). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.