memory_save_tool_event · Mementos MCP: Risk & Policy

WHAT IT DOES

What memory_save_tool_event does on Mementos

AI agents use memory_save_tool_event 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_save_tool_event needs a policy

This tool creates new memory records (events and lessons) and modifies shared memory state. These are write operations typical of a logging/memory system—reversible via update or deletion mechanisms (as evidenced by sibling tools like 'bulk_forget' and 'entity_delete').

From the tool's definition Tool description states 'Record a tool call event' and 'saves a lesson as a shared memory', indicating creation and modification of event/memory records without permanent deletion.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

memory_save_tool_event Rate-limited

memory_save_tool_event 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_save_tool_event": {
      "limits": [
        {
          "counter": "memory_save_tool_event_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_save_tool_event

What does the memory_save_tool_event tool do? +

Record a tool call event (success/failure, latency, tokens). Optionally saves a lesson as a shared 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_save_tool_event? +

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

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

Can I rate-limit memory_save_tool_event? +

Yes. Add a rate_limit block to the memory_save_tool_event 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_save_tool_event completely? +

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

memory_save_tool_event 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.