webhook_update · Mementos MCP: Risk & Policy

WHAT IT DOES

What webhook_update does on Mementos

AI agents use webhook_update 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_update needs a policy

This tool modifies webhook configuration by updating persistence settings. While it creates or modifies data reversibly (webhooks can be re-enabled or updated again), it does not retrieve data (Read), execute arbitrary code (Execute), irreversibly delete data (Destructive), or move money (Financial).

From the tool's definition Tool name 'webhook_update' and description states 'Enable, disable, or update a persisted webhook hook.' The operations of enabling, disabling, and updating are write operations that modify webhook configuration state.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

webhook_update Rate-limited

webhook_update 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_update": {
      "limits": [
        {
          "counter": "webhook_update_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_update

What does the webhook_update tool do? +

Enable, disable, or update a persisted webhook hook. 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_update? +

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

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

Can I rate-limit webhook_update? +

Yes. Add a rate_limit block to the webhook_update 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_update completely? +

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

webhook_update 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.