update_calendar · MCP Apple Reminders MCP: Risk & Policy

WHAT IT DOES

What update_calendar does on MCP Apple Reminders

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

WHY IT NEEDS A POLICY

Why update_calendar needs a policy

The tool modifies calendar-related data (likely reminder dates, times, or calendar associations) reversibly. While the description is empty, the name and server context indicate a Write operation. Severity is medium rather than high because calendar updates are typically reversible and have limited blast radius compared to destructive or execute operations.

From the tool's definition Tool name 'update_calendar' paired with server context showing 'update' capability for reminders and lists. Server description explicitly lists 'update' as a supported operation for reminders/lists on macOS.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

update_calendar Rate-limited

update_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": {
    "update_calendar": {
      "limits": [
        {
          "counter": "update_calendar_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 MCP Apple Reminders, so you can run agents against it safely.

FAQ

Questions about update_calendar

What does the update_calendar tool do? +

update_calendar. It is categorised as a Write tool in the MCP Apple Reminders MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on update_calendar? +

Register the MCP Apple Reminders MCP server in PolicyLayer and add a rule for update_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 MCP Apple Reminders. Nothing to install.

What risk level is update_calendar? +

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

Can I rate-limit update_calendar? +

Yes. Add a rate_limit block to the update_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 update_calendar completely? +

Set action: deny in the PolicyLayer policy for update_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 update_calendar? +

update_calendar is provided by the MCP Apple Reminders MCP server (rex/mcp-apple-reminders). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.