entity_update · Mementos MCP: Risk & Policy

WHAT IT DOES

What entity_update does on Mementos

AI agents use entity_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 entity_update needs a policy

Updates are reversible writes that modify stored entities without destroying data or executing external operations. Medium severity reflects potential for disruption to agent memory/state if misused, but limited blast radius since changes can be rolled back and no financial or destructive consequences are inherent.

From the tool's definition Tool name 'entity_update' and description 'Update an entity' indicate modification of existing data in the memory system. No deletion occurs, and changes are reversible.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

entity_update Rate-limited

entity_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": {
    "entity_update": {
      "limits": [
        {
          "counter": "entity_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 entity_update

What does the entity_update tool do? +

Update an entity. 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 entity_update? +

Register the Mementos MCP server in PolicyLayer and add a rule for entity_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 entity_update? +

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

Can I rate-limit entity_update? +

Yes. Add a rate_limit block to the entity_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 entity_update completely? +

Set action: deny in the PolicyLayer policy for entity_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 entity_update? +

entity_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.