update_memento · MCP Memento MCP: Risk & Policy

WHAT IT DOES

What update_memento does on MCP Memento

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

WHY IT NEEDS A POLICY

Why update_memento needs a policy

This tool modifies existing records in a knowledge base reversibly. It is a Write operation—data can be updated or corrected without permanent loss. It does not delete data (Destructive), execute arbitrary code (Execute), move money (Financial), or trigger external side effects. The low severity reflects that misuse would only corrupt one memento's contents rather than cause cascading damage across the system.

From the tool's definition Tool name 'update_memento' and description 'Update an existing memento' indicate modification of stored data. The MCP Memento server is described as a 'persistent long-term memory' system for storing solutions, facts, and decisions.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

update_memento Rate-limited

update_memento 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": {
    "update_memento": {
      "limits": [
        {
          "counter": "update_memento_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 MCP Memento, so you can run agents against it safely.

FAQ

Questions about update_memento

What does the update_memento tool do? +

Update an existing memento. It is categorised as a Write tool in the MCP Memento MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on update_memento? +

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

What risk level is update_memento? +

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

Can I rate-limit update_memento? +

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

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

update_memento is provided by the MCP Memento MCP server (x-hannibal/mcp-memento). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.