create_webhook · Posterly MCP: Risk & Policy

WHAT IT DOES

What create_webhook does on Posterly

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

WHY IT NEEDS A POLICY

Why create_webhook needs a policy

This tool creates a new webhook resource that will persistently send events to an external URL, modifying the system configuration. It is Write category rather than Destructive because webhook creation is reversible (webhooks can be deleted). It is elevated to medium severity because misconfiguration could cause unintended data exfiltration or trigger undesired external operations.

From the tool's definition Tool description explicitly states 'Create a webhook subscription' and 'WRITE WITH OUTBOUND SIDE EFFECTS', indicating irreversible creation of a webhook that will trigger external HTTP requests to a specified target URL.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

create_webhook Rate-limited

create_webhook 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": {
    "create_webhook": {
      "limits": [
        {
          "counter": "create_webhook_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 Posterly, so you can run agents against it safely.

FAQ

Questions about create_webhook

What does the create_webhook tool do? +

Create a webhook subscription for post/account/analytics events. WRITE WITH OUTBOUND SIDE EFFECTS: show the user the target URL, workspace, events, and active state, then get explicit confirmation before calling. The response includes the signing secret once. It is categorised as a Write tool in the Posterly MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on create_webhook? +

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

What risk level is create_webhook? +

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

Can I rate-limit create_webhook? +

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

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

create_webhook is provided by the Posterly MCP server (posterly-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.