memory_pin · Mementos MCP: Risk & Policy

WHAT IT DOES

What memory_pin does on Mementos

AI agents use memory_pin 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 memory_pin needs a policy

Pinning/unpinning a memory changes its state or retrieval priority but does not create, delete, or destroy data. It is a reversible Write operation. Severity is medium because misuse could suppress important memories from an agent's accessible context, potentially affecting decision-making, but the operation itself is not destructive and can be undone.

From the tool's definition Tool name 'memory_pin' and description 'Pin or unpin a memory' indicates modification of metadata (pin state) associated with stored memories. This is a reversible change—pinning and unpinning can be toggled.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

memory_pin Rate-limited

memory_pin 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": {
    "memory_pin": {
      "limits": [
        {
          "counter": "memory_pin_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 memory_pin

What does the memory_pin tool do? +

Pin or unpin a memory by ID or key. No version needed. 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 memory_pin? +

Register the Mementos MCP server in PolicyLayer and add a rule for memory_pin: 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 memory_pin? +

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

Can I rate-limit memory_pin? +

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

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

memory_pin 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.