subscribe · Nexus Memory MCP: Risk & Policy

WHAT IT DOES

What subscribe does on Nexus Memory

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

WHY IT NEEDS A POLICY

Why subscribe needs a policy

The subscribe tool creates or registers a new webhook subscription, which is a reversible data modification. It does not delete data (Destructive), execute arbitrary code (Execute), move money (Financial), or merely read data (Read). However, registering webhooks could enable exfiltration if a malicious URL is registered, placing this at medium severity rather than low.

From the tool's definition Tool name is 'subscribe' and description indicates it 'Register[s] a webhook URL to receive HTTP POST notifications when' — this creates a new subscription record (write operation).

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

subscribe Rate-limited

subscribe 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": {
    "subscribe": {
      "limits": [
        {
          "counter": "subscribe_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 Nexus Memory, so you can run agents against it safely.

FAQ

Questions about subscribe

What does the subscribe tool do? +

Register a webhook URL to receive HTTP POST notifications when. It is categorised as a Write tool in the Nexus Memory MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on subscribe? +

Register the Nexus Memory MCP server in PolicyLayer and add a rule for subscribe: 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 Nexus Memory. Nothing to install.

What risk level is subscribe? +

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

Can I rate-limit subscribe? +

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

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

subscribe is provided by the Nexus Memory MCP server (neboy72/nexus-memory). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.