iCloud CalDAV MCP Connector

An HTTP Model Context Protocol (MCP) server exposing iCloud Calendar (CalDAV) tools so MCP-aware clients (e.g., ChatGPT custom connectors, IDEs) can list calendars, read events, and create/update/delete events using an iCloud app-specific password.

Unofficial. Calendar only. Keep this service private; it forwards your iCloud app-specific password to Apple’s CalDAV endpoint.

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Why did I build this?

I built this to use in ChatGPT Custom Connector, so I can change my iCloud Calendar compared to changing it manually. Came up with this idea on a Friday night before a TOP Pset was due, and this turned out to be a fun 1-day project.

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Features

• HTTP MCP server (/mcp) + GET /health
• Tools (default write-capable profile):
  • list_calendars()
  • list_calendars_with_events(start, end, expand_recurring=True)
  • list_events(calendar_name_or_url, start, end, expand_recurring=True)
  • create_event(calendar_name_or_url, summary, start, end, tzid?, description?, location?, recurrence?)
  • update_event(calendar_name_or_url, uid, summary?, start?, end?, tzid?, description?, location?, recurrence?, clear_recurrence=False)
  • delete_event(calendar_name_or_url, uid)
• Tools (Deep Research read-only profile):
  • search(query) → basic text search over SUMMARY/DESCRIPTION in a time window
  • fetch(ids) → fetch raw text/calendar ICS blobs for search results
• ISO datetime input (YYYY-MM-DDTHH:MM:SS, with optional Z or timezone offset)
• Minimal ICS generation (summary/description escaping), UID matching across a ±3-year window

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Requirements

• Python 3.11+
• Apple ID (email identity, not phone number)
• iCloud app-specific password (revocable)
• Network access to https://caldav.icloud.com

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Environment

Create a .env next to server.py (auto-loaded):

APPLE_ID=you@example.com                 # Use your Apple ID email
ICLOUD_APP_PASSWORD=xxxx-xxxx-xxxx-xxxx  # App-specific password
CALDAV_URL=https://caldav.icloud.com     # optional, default shown
HOST=127.0.0.1                           # optional
PORT=8000                                # optional
TZID=America/New_York                    # default TZ for new/edited events

# Deep Research: read-only profile (optional)
DR_PROFILE=0                             # Set to 1 to enable DR mode (default 0)
SCAN_DAYS=1095                           # Time window (days) scanned by DR search/fetch (default ~3 years)

Required: APPLE_ID, ICLOUD_APP_PASSWORD.

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Quick Start (local)

python -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

# Ensure .env exists (see above), then:
python server.py
# -> Listening on http://127.0.0.1:8000
curl http://127.0.0.1:8000/health   # OK

MCP endpoint: http://127.0.0.1:8000/mcp

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Tool Reference (functional details)

list_calendars() -> List[Calendar]

Returns:

• name: str | null
• url: str (preferred identifier for other calls)
• id: str | null

list_calendars_with_events(start, end, expand_recurring=True) -> List[Calendar]

Returns only the calendars that contain at least one event in the given time window.

Args

• start, end: str — ISO datetimes; search is [start, end)
• expand_recurring: bool — treat recurring series as concrete instances

Each returned calendar has the same shape as list_calendars().

list_events(calendar_name_or_url, start, end, expand_recurring=True) -> List[Event]

Args

• calendar_name_or_url: str — display name or full CalDAV URL
• start, end: str — ISO datetimes; search is [start, end)
• expand_recurring: bool — include concrete instances of recurring series

Returns each event with:

• uid: str
• summary: str
• start: str (ISO)
• end: str | null (ISO)
• raw: str (original ICS text)

create_event(calendar_name_or_url, summary, start, end, tzid?, description?, location?, recurrence?) -> str

Creates a minimal VEVENT.

• tzid defaults to TZID env if omitted; naive datetimes are assumed in that zone and stored as UTC.

• description is optional; omit or pass null to skip it.

• location is optional; omit or pass null to skip it.

• recurrence (optional) describes how the event should repeat, for example:

  {
      "frequency": "weekly",              // daily | weekly | monthly | yearly | custom
      "interval": 1,                       // optional, default 1
      "by_weekday": ["MO", "WE"],         // optional; for weekly/custom
      "by_monthday": [1, 15],             // optional; for monthly/custom
      "end": {                            // optional end condition
          "type": "on_date",              // or "after_occurrences"
          "date": "2025-12-31"            // when type == "on_date"
          // or: "count": 10               // when type == "after_occurrences"
      }
      // for custom frequency you can pass a raw RRULE:
      // "frequency": "custom",
      // "rrule": "FREQ=MONTHLY;BYDAY=MO,TU;BYSETPOS=1"
  }

• Returns the generated uid (random hex + @chatgpt-mcp).

update_event(calendar_name_or_url, uid, summary?, start?, end?, tzid?, description?, location?, recurrence?, clear_recurrence=False) -> bool

Updates the whole event identified by uid (for recurring events this updates the series VEVENT, not a single instance).

• Preserves any omitted fields from the original component.
• location:
  • If omitted (null / not provided), keeps the existing location.
  • If provided as a non-empty string, updates the event’s location.
  • If provided as an empty string, clears the event’s location.
• recurrence:
  • If provided, replaces any existing RRULE using the same shape as in create_event.
• clear_recurrence:
  • If True, removes any RRULE and converts the event back to a single non-recurring instance.
  • If True and recurrence is also provided, clear_recurrence wins (no recurrence).
• Returns True on success, False if uid not found in ±3-year window.

delete_event(calendar_name_or_url, uid) -> bool

Deletes the first matching uid in a ±3-year window.

• Returns True if deleted, False if not found.

Date/Time Notes

• Accepts naive or Z/offset datetimes (YYYY-MM-DDTHH:MM:SS, optionally Z or -04:00 etc.)
• New/edited events emit DTSTART;TZID=... and DTEND;TZID=... using provided tzid or TZID env
• Updates attempt to reuse the original TZID when present
• LOCATION is emitted when location is provided and non-empty; passing an empty string when updating an event removes the existing location.

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Deep Research read-only mode

Set DR_PROFILE=1 to run a read-only tool set for Deep Research. This exposes only:

• search(query) -> [{ id, title, snippet }]
• fetch(ids) -> [{ id, mimeType: 'text/calendar', content }]

Example:

DR_PROFILE=1 HOST=127.0.0.1 PORT=8000 python server.py

Notes:

• Write tools (list_events/create_event/update_event/delete_event) are disabled in this mode.
• SCAN_DAYS controls the search window around “now” (default: 1095 days ≈ 3 years).
• Keep this service private or add auth

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Example (programmatic client)

import asyncio, json
from fastmcp import Client

MCP_URL = "http://127.0.0.1:8000/mcp"
CAL_URL = "<paste one of your calendar URLs>"

def unwrap(res):
    sc = getattr(res, "structured_content", None)
    if isinstance(sc, dict) and "result" in sc:
        return sc["result"]
    return json.loads(res.content[0].text)

async def main():
    async with Client(MCP_URL) as c:
        cals = unwrap(await c.call_tool("list_calendars", {"confirm": True}))
        print("Calendars:", cals[:2])

        evs = unwrap(await c.call_tool("list_events", {
            "calendar_name_or_url": CAL_URL,
            "start": "2025-09-01T00:00:00",
            "end":   "2025-10-01T00:00:00",
            "expand_recurring": True
        }))
        print("Events:", len(evs))

        uid = unwrap(await c.call_tool("create_event", {
            "calendar_name_or_url": CAL_URL,
            "summary":"Demo",
            "start":"2025-09-29T15:00:00",
            "end":"2025-09-29T15:30:00",
            "tzid":"America/New_York",
            "location": "Bobst Library"
        }))
        print("Created:", uid)

asyncio.run(main())

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Deployment / Public HTTPS

To use this with ChatGPT Custom Connectors you need a public HTTPS endpoint that forwards to your local server.

See DEPLOY.md for:

• Cloudflare Tunnel (stable hostname, free)
• ngrok (quick test)
• VPS + Caddy/Nginx (permanent)

Security: add auth (Cloudflare Access, Basic Auth proxy, IP allowlist). Do NOT expose this unauthenticated; it holds live calendar write access. You need a public HTTPS URL that forwards to your local http://127.0.0.1:8000.

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Troubleshooting

Symptom	Likely Cause / Fix
401 Unauthorized	Wrong Apple ID or app-specific password; ensure .env uses email, not phone.
Empty event results	Wrong calendar URL or time window; remember end is exclusive.
Update/Delete no-ops	UID not in ±3-year scan window or different calendar than you’re querying.
Timezone drift	Pass tzid explicitly (e.g., America/New_York) or use UTC ...Z.

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Security

• Use app-specific passwords and rotate as needed
• Keep this server private (tunnel ACLs, IP allowlists, auth proxy)
• This project rewrites minimal VEVENTs; advanced fields (attendees, alarms, recurrence exceptions) are not preserved on update

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License

MIT License.

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Happy scheduling, I hope this helps!