calendar.list_sources

THE RISK

Low Risk

Why calendar.list_sources needs a policy

This tool retrieves metadata about calendar sources without side effects. It allows discovery of calendar accounts available on the device, but does not create, modify, delete, or execute any operations. It is the least risky category of operation.

From the tool's definition Tool name contains 'list' and description states 'List calendar sources/accounts' — a pure enumeration operation with no modification, deletion, or execution.

Documented attack patterns abuse exactly the kind of access calendar.list_sources gives an agent:

POLICY

How to control calendar.list_sources

PolicyLayer is an MCP gateway — it sits between your AI agents and Nucleus Apple, and nothing reaches the server without passing your rules. This is the rule we recommend for calendar.list_sources:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "calendar.list_sources": {}
  }
}

calendar.list_sources is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

Create a free account and register Nucleus Apple — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

CAP THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Nucleus Apple tools

Destructive calendar.delete_event Delete a calendar event. Destructive notes.delete_note Delete a note. Destructive reminders.delete_reminder Delete a reminder. Write notes.save_attachment Export an attachment to a file path. Write calendar.create_event Create a calendar event. Write calendar.update_event Update an existing calendar event. Write notes.add_attachment Add attachment(s) to a note from local file paths. Write notes.create_note Create a new note.

All 30 Nucleus Apple tools →

Read tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about calendar.list_sources

What does the calendar.list_sources tool do? +

List calendar sources/accounts. It is categorised as a Read tool in the Nucleus Apple MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on calendar.list_sources? +

Register the Nucleus Apple MCP server in PolicyLayer and add a rule for calendar.list_sources: 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 Nucleus Apple. Nothing to install.

What risk level is calendar.list_sources? +

calendar.list_sources is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit calendar.list_sources? +

Yes. Add a rate_limit block to the calendar.list_sources 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 calendar.list_sources completely? +

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

calendar.list_sources is provided by the Nucleus Apple MCP server (zish-rob-crur/nucleus-apple-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Nucleus Apple tool call.

Start from Nucleus Apple, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →