pin_memory · Agent Bus MCP: Risk & Policy

WHAT IT DOES

What pin_memory does on Agent Bus

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

WHY IT NEEDS A POLICY

Why pin_memory needs a policy

This tool creates or modifies metadata about memories within the agent collaboration bus by changing their visibility/priority state in handoff communications. While reversible (unpinning would undo it), it alters system state and could influence how information is presented to other agents.

From the tool's definition Tool description explicitly states it modifies session state by pinning a memory to make it surface in a 'pinned handoff section' — a direct data modification action.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

pin_memory Rate-limited

pin_memory 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": {
    "pin_memory": {
      "limits": [
        {
          "counter": "pin_memory_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 Agent Bus, so you can run agents against it safely.

FAQ

Questions about pin_memory

What does the pin_memory tool do? +

Pin a memory so session_brief surfaces it in the pinned handoff section. It is categorised as a Write tool in the Agent Bus MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on pin_memory? +

Register the Agent Bus MCP server in PolicyLayer and add a rule for pin_memory: 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 Agent Bus. Nothing to install.

What risk level is pin_memory? +

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

Can I rate-limit pin_memory? +

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

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

pin_memory is provided by the Agent Bus MCP server (mustaphasteph/agent-bus). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.