create_event · Fastmail Calendar MCP Server MCP

WHAT IT DOES

What create_event does on Fastmail Calendar MCP Server

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

WHY IT NEEDS A POLICY

Why create_event needs a policy

The create_event tool creates new calendar entries, which is a Write operation—it modifies data (adds events) but is reversible (events can be deleted or updated via sibling tools like delete_event or update_event).

From the tool's definition Tool description explicitly states 'Create a new calendar event' with 'specified title, times, and optional description/location', which is a reversible create operation on calendar data.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

create_event Rate-limited

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": {
    "create_event": {
      "limits": [
        {
          "counter": "create_event_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 Fastmail Calendar MCP Server, so you can run agents against it safely.

FAQ

Questions about create_event

What does the create_event tool do? +

Create a new calendar event. PREREQUISITE: You must first call list_calendars to get the calendarUrl. Creates an event with the specified title, times, and optional description/location. It is categorised as a Write tool in the Fastmail Calendar MCP Server 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_event? +

Register the Fastmail Calendar MCP Server MCP server in PolicyLayer and add a rule for 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 Fastmail Calendar MCP Server. Nothing to install.

What risk level is create_event? +

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

Can I rate-limit create_event? +

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

Set action: deny in the PolicyLayer policy for 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 create_event? +

create_event is provided by the Fastmail Calendar MCP Server MCP server (nova-3951/fastmail-calendar-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.