register_machine · Mementos MCP: Risk & Policy

WHAT IT DOES

What register_machine does on Mementos

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

WHY IT NEEDS A POLICY

Why register_machine needs a policy

This tool creates or modifies data in a machine registry (Write category). While registration itself is not destructive, it establishes a record that an AI agent could use to register unauthorized machines or create confusion about system identity.

From the tool's definition register_machine registers a machine in the mementos machine registry, creating or updating a machine record. The description states 'Auto-detects hostname. Idempotent by hostname,' indicating it creates/updates persistent state in a registry.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

register_machine Rate-limited

register_machine 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": {
    "register_machine": {
      "limits": [
        {
          "counter": "register_machine_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 Mementos, so you can run agents against it safely.

FAQ

Questions about register_machine

What does the register_machine tool do? +

Register the current machine in the mementos machine registry. Auto-detects hostname. Idempotent by hostname. It is categorised as a Write tool in the Mementos MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on register_machine? +

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

What risk level is register_machine? +

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

Can I rate-limit register_machine? +

Yes. Add a rate_limit block to the register_machine 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 register_machine completely? +

Set action: deny in the PolicyLayer policy for register_machine. 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 register_machine? +

register_machine is provided by the Mementos MCP server (@hasna/mementos). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.