entity_merge · Mementos MCP: Risk & Policy

WHAT IT DOES

What entity_merge does on Mementos

AI agents use entity_merge 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_merge needs a policy

The tool modifies existing data by consolidating entities and relocating their relations and links. While the operation is technically reversible (the source entity's data is moved, not deleted), it constitutes a Write action because it permanently alters the state of entities and their interconnections.

From the tool's definition Tool description states it will 'Merge source entity into target' and 'Moves all relations and memory links' — these are irreversible data transformations that modify the structure and associations of stored entities.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

entity_merge Rate-limited

entity_merge 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_merge": {
      "limits": [
        {
          "counter": "entity_merge_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_merge

What does the entity_merge tool do? +

Merge source entity into target. Moves all relations and memory links. 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_merge? +

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

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

Can I rate-limit entity_merge? +

Yes. Add a rate_limit block to the entity_merge 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_merge completely? +

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

entity_merge 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.