cal_create_event · Hermes Google MCP: Risk & Policy

WHAT IT DOES

What cal_create_event does on Hermes Google

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

WHY IT NEEDS A POLICY

Why cal_create_event needs a policy

This tool creates new calendar events, which is a Write operation that modifies data. While the user confirmation requirement reduces severity from high to medium, an AI agent with access could still create numerous unwanted calendar entries, spam calendars, or schedule misleading appointments that affect the user's time management and potentially impact others who view shared calendars.

From the tool's definition Tool name 'cal_create_event' and description 'Create a calendar event' indicate irreversible creation of calendar data. The phrase 'Requires user confirmation before calling' mitigates but does not eliminate the risk.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

cal_create_event Rate-limited

cal_create_event 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": {
    "cal_create_event": {
      "limits": [
        {
          "counter": "cal_create_event_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Hermes Google, so you can run agents against it safely.

FAQ

Questions about cal_create_event

What does the cal_create_event tool do? +

Create a calendar event. Requires user confirmation before calling. It is categorised as a Write tool in the Hermes Google MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on cal_create_event? +

Register the Hermes Google MCP server in PolicyLayer and add a rule for cal_create_event: 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 Hermes Google. Nothing to install.

What risk level is cal_create_event? +

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

Can I rate-limit cal_create_event? +

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

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

cal_create_event is provided by the Hermes Google MCP server (jimmy-larsson/hermes-google). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.