memory_update · Mementos MCP: Risk & Policy

WHAT IT DOES

What memory_update does on Mementos

AI agents use memory_update 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_update needs a policy

The tool modifies stored memory records but the operation is reversible (can be updated again or reverted), placing it in the Write category rather than Destructive. Severity is medium because unauthorized memory updates could corrupt an AI agent's knowledge base and affect decision-making, but the impact is limited to the memory system itself without triggering financial or external system consequences.

From the tool's definition Tool description 'Update a memory' and name 'memory_update' perform a reversible modification of existing data.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

memory_update Rate-limited

memory_update 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_update": {
      "limits": [
        {
          "counter": "memory_update_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_update

What does the memory_update tool do? +

Update a memory. 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_update? +

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

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

Can I rate-limit memory_update? +

Yes. Add a rate_limit block to the memory_update 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_update completely? +

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

memory_update 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.