webhook_create · Mementos MCP: Risk & Policy

WHAT IT DOES

What webhook_create does on Mementos

AI agents use webhook_create 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 webhook_create needs a policy

This tool creates a new persistent webhook resource, which is a Write operation—it modifies the system state by adding a new entity. Severity is high because webhooks can forward sensitive data or context to attacker-controlled URLs if an AI agent is manipulated into creating webhooks pointing to malicious endpoints.

From the tool's definition Tool name 'webhook_create' and description 'Create a persistent HTTP webhook hook' indicate irreversible creation of a new resource that persists in the system. The webhook will establish an ongoing communication channel that POSTs data to an external URL.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

webhook_create Rate-limited

webhook_create 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": {
    "webhook_create": {
      "limits": [
        {
          "counter": "webhook_create_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 webhook_create

What does the webhook_create tool do? +

Create a persistent HTTP webhook hook. The URL will be POSTed with the hook context as JSON. 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 webhook_create? +

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

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

Can I rate-limit webhook_create? +

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

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

webhook_create 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.