subscribe_calendar · Calendar MCP: Risk & Policy

WHAT IT DOES

What subscribe_calendar does on Calendar Mcp

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

WHY IT NEEDS A POLICY

Why subscribe_calendar needs a policy

Subscribing to push notifications creates a new webhook/subscription resource on the calendar service. This is a reversible write operation (subscriptions expire after 7 days and can presumably be deleted). It does not read existing data, execute arbitrary code, delete anything, or move money.

From the tool's definition Subscribe to push notifications for calendar changes (7-day expiry)

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

subscribe_calendar Rate-limited

subscribe_calendar 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_calendar": {
      "limits": [
        {
          "counter": "subscribe_calendar_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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Instant setup, no code required.

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

FAQ

Questions about subscribe_calendar

What does the subscribe_calendar tool do? +

Subscribe to push notifications for calendar changes (7-day expiry). It is categorised as a Write tool in the Calendar Mcp 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_calendar? +

Register the Calendar MCP server in PolicyLayer and add a rule for subscribe_calendar: 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 Calendar Mcp. Nothing to install.

What risk level is subscribe_calendar? +

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

Can I rate-limit subscribe_calendar? +

Yes. Add a rate_limit block to the subscribe_calendar 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_calendar completely? +

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

subscribe_calendar is provided by the Calendar MCP server (ydrogen/calendar-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.