memento_begin_session · Memento MCP: Risk & Policy

WHAT IT DOES

What memento_begin_session does on Memento

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

WHY IT NEEDS A POLICY

Why memento_begin_session needs a policy

This tool creates a new session and closes any currently active session, which is a state-modifying write operation. Closing an active session may cause loss of unsaved session state, but is not fully irreversible in the destructive sense. Marked deprecated, which slightly lowers confidence. The blast radius is medium since it affects the active session context for the AI agent.

From the tool's definition 'Start a new Memento session for this workspace (closes any active session)'

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

memento_begin_session Rate-limited

memento_begin_session 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": {
    "memento_begin_session": {
      "limits": [
        {
          "counter": "memento_begin_session_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Memento, so you can run agents against it safely.

FAQ

Questions about memento_begin_session

What does the memento_begin_session tool do? +

[DEPRECATED] Start a new Memento session for this workspace (closes any active session). It is categorised as a Write tool in the 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 memento_begin_session? +

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

What risk level is memento_begin_session? +

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

Can I rate-limit memento_begin_session? +

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

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

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