CalDAV MCP Server

CalDAV MCP Server is a Model Context Protocol server for managing iCloud Calendar events, including native support for multiple VALARM reminders on one event.

iCloud Calendar is the only provider officially supported and manually validated in the first release. The server works with any MCP client that supports stdio or Streamable HTTP.

This independent project is not affiliated with, authorized, sponsored, or approved by Apple Inc. Apple and iCloud are trademarks of their respective owner.

Navigation

• About
• Features
• MCP tools
• Tech stack
• Installation
• Configuration
• MCP client setup
• Verification
• Limitations
• Contributing

About

The server connects one configured account to iCloud through CalDAV. It discovers the account's calendars and exposes normalized read and write operations through MCP.

Updates preserve the complete iCalendar resource, including unknown properties, Apple extensions, VTIMEZONE, recurrence exceptions, and alarms omitted from a patch. Writes use opaque resource identifiers and ETags instead of assuming that a CalDAV filename matches an event UID.

Calendar resources are processed in memory. The server has no telemetry and no application database, and raw iCalendar is returned only when explicitly requested.

Features

• Discovers calendars available to the configured iCloud account.
• Lists events in semi-open time ranges and expands recurring occurrences.
• Creates timed, all-day, and recurring events.
• Supports zero, one, or multiple display alarms per event.
• Emits the Apple alarm extensions expected by iCloud Calendar.
• Reads events by opaque resource ID or by calendar ID and UID.
• Applies partial updates while preserving omitted and unknown iCalendar data.
• Uses ETags for optimistic concurrency on updates and deletions.
• Rejects isolated recurrence mutations instead of changing the complete series.
• Redacts credentials, raw calendar content, and CalDAV paths from logs and errors.
• Runs as a non-root container with a read-only root filesystem configuration.
• Supports stdio and Streamable HTTP MCP transports.

MCP tools

list_calendars

Lists the calendars discovered for the configured account. Each result includes an opaque calendar_id, display name, description, timezone, and best-effort write status.

list_events

Lists events in a semi-open interval and expands recurring occurrences. The maximum range is 366 days, the default page size is 100, and the maximum page size is 500.

Example input:

{
  "calendar_id": "opaque-calendar-id",
  "start": "2026-09-01T00:00:00Z",
  "end": "2026-10-01T00:00:00Z",
  "timezone": "Europe/Berlin",
  "limit": 100
}

get_event

Reads an event by resource_id, or by a calendar_id and UID pair. Raw iCalendar is excluded by default and can be requested with include_raw_ical: true for controlled diagnostics.

create_event

Creates an event and reads back the representation stored by the server.

Timed event with two alarms:

{
  "calendar_id": "opaque-calendar-id",
  "summary": "Buy Shinkansen tickets",
  "start": {
    "date_time": "2026-09-06T03:00:00+02:00",
    "timezone": "Europe/Berlin"
  },
  "end": {
    "date_time": "2026-09-06T03:30:00+02:00",
    "timezone": "Europe/Berlin"
  },
  "description": "Smart-EX",
  "location": null,
  "alarms": [
    { "minutes_before": 1440, "action": "DISPLAY" },
    { "minutes_before": 0, "action": "DISPLAY" }
  ],
  "rrule": null
}

All-day event with an exclusive end date:

{
  "calendar_id": "opaque-calendar-id",
  "summary": "Trip",
  "start": { "date": "2026-09-06" },
  "end": { "date": "2026-09-08" },
  "alarms": []
}

Recurring events accept an RFC 5545 rule without the RRULE: prefix:

{
  "calendar_id": "opaque-calendar-id",
  "summary": "Weekly planning",
  "start": {
    "date_time": "2026-09-07T09:00:00+02:00",
    "timezone": "Europe/Berlin"
  },
  "end": {
    "date_time": "2026-09-07T09:30:00+02:00",
    "timezone": "Europe/Berlin"
  },
  "rrule": "FREQ=WEEKLY;BYDAY=MO;COUNT=10"
}

update_event

Patches an event or complete recurring series. Omitted fields are preserved, null removes a nullable field, and alarms: [] removes all alarms. An optional expected_etag prevents overwriting a newer server version.

delete_event

Deletes an event or complete recurring series, optionally requiring an observed ETag. Deleting a single expanded occurrence is not supported in the current release.

Tech stack

• Node.js 24+
• TypeScript with strict project rules
• Model Context Protocol TypeScript SDK
• tsdav
• ical.js
• Zod
• Vitest
• pnpm
• Docker

Installation

Prerequisites

• An iCloud account with Calendar enabled.
• Two-factor authentication enabled for the Apple Account.
• An app-specific password.
• Docker and Docker Compose for container deployment, or Node.js 24+ and pnpm for a local installation.

Docker Compose

The recommended installation uses the published multi-architecture image:

ghcr.io/lukegskw/caldav-mcp:latest

Download the Compose example:

curl -O https://raw.githubusercontent.com/lukegskw/caldav-mcp/main/compose.example.yaml

Provide the Apple Account email and app-specific password, then start the service:

export CALDAV_USERNAME='user@example.com'
export CALDAV_PASSWORD='xxxx-xxxx-xxxx-xxxx'
docker compose -f compose.example.yaml up -d

To publish a different host port, set:

export CALDAV_MCP_PUBLISHED_PORT=18100
docker compose -f compose.example.yaml up -d

The latest tag follows the newest successful build from the default branch. For a controlled deployment or rollback, replace it in the Compose file with a published version or immutable sha-* tag.

The Streamable HTTP endpoint will be available at:

http://<host>:8100/mcp

The host port can change without changing port 8100 inside the container. No persistent volume is required; calendar data remains in iCloud.

Docker run

The same hardened container configuration can be started directly:

docker run -d \
  --name caldav-mcp \
  --restart unless-stopped \
  --read-only \
  --user 10001:10001 \
  --cap-drop ALL \
  --security-opt no-new-privileges:true \
  --tmpfs /tmp:size=16m,mode=1777 \
  -e CALDAV_PROVIDER=icloud \
  -e CALDAV_USERNAME \
  -e CALDAV_PASSWORD \
  -e CALDAV_MCP_TRANSPORT=streamable-http \
  -e CALDAV_MCP_HOST=0.0.0.0 \
  -p 8100:8100 \
  ghcr.io/lukegskw/caldav-mcp:latest

Build the container from source

Building locally is optional. Prefer the published image unless you need to modify or audit the container build.

git clone https://github.com/lukegskw/caldav-mcp.git
cd caldav-mcp
docker buildx build --load -t caldav-mcp:local .

Local Node.js installation

git clone https://github.com/lukegskw/caldav-mcp.git
cd caldav-mcp
pnpm install --frozen-lockfile
cp .env.example .env
pnpm build
pnpm start -- --transport stdio

In stdio mode, stdout is reserved exclusively for MCP messages. To run Streamable HTTP locally:

CALDAV_MCP_TRANSPORT=streamable-http pnpm start

Configuration

All settings use the CALDAV_ or CALDAV_MCP_ prefix.

Variable	Required	Default	Description
CALDAV_PROVIDER	No	icloud	Provider policy. iCloud is the supported profile.
CALDAV_URL	No	https://caldav.icloud.com	CalDAV discovery URL.
CALDAV_USERNAME	Yes	None	Apple Account email.
CALDAV_PASSWORD	Yes	None	App-specific password, not the account password.
CALDAV_MCP_TRANSPORT	No	stdio	stdio or streamable-http.
CALDAV_MCP_HOST	No	0.0.0.0	HTTP bind address.
CALDAV_MCP_PORT	No	8100	HTTP listening port.
CALDAV_MCP_LOG_LEVEL	No	INFO	Application log level.
CALDAV_MCP_REQUEST_TIMEOUT_MS	No	30000	CalDAV request timeout.

The core retains an experimental generic provider policy and configurable URL to keep Apple extensions isolated from the shared iCalendar implementation. No compatibility with other providers is currently claimed.

Secrets must be supplied through the deployment platform or environment. Never commit .env, pass credentials as MCP tool arguments, or include them in diagnostic reports.

MCP client setup

For any MCP client that accepts Streamable HTTP server definitions, configure the URL:

mcp_servers:
  caldav:
    url: http://<host>:8100/mcp

If the client shares the Compose network, use the service name and internal port:

mcp_servers:
  caldav:
    url: http://caldav-mcp:8100/mcp

For clients that launch local stdio servers, configure the command to run node /absolute/path/to/caldav-mcp/dist/main.js with the required environment variables.

Configuration formats differ between MCP clients. Consult the client's documentation for its exact schema and reload or restart it after changing the server definition.

Verification

Check the container state and logs:

docker compose -f compose.example.yaml ps
docker compose -f compose.example.yaml logs caldav-mcp

The container should report healthy. The TCP healthcheck validates the server process, not iCloud credentials.

Run the repository verification suite:

pnpm install --frozen-lockfile
pnpm format:check
pnpm lint
pnpm typecheck
pnpm test:unit
pnpm test:integration
pnpm build

Finally, connect with an MCP client and confirm that all six tools are listed. Before a release, run the dedicated iCloud manual validation against a test calendar.

Limitations

• One iCloud account is configured per server process or container.
• The Streamable HTTP endpoint has no authentication in the current release. Restrict it to a trusted LAN, VPN, or private container network; do not expose it directly to the internet.
• Individual recurrence occurrences are read-only. Updating or deleting the complete series is supported.
• Only ACTION:DISPLAY alarms are created.
• Individual iCalendar resources are limited to 5 MiB.
• Event list ranges are limited to 366 days and pages to 500 results.
• Events may contain at most 20 alarms.
• Attendee scheduling is outside the current scope.
• Providers other than iCloud are not officially supported.

See troubleshooting for discovery, authentication, ETag, and Apple extension guidance. Review SECURITY.md before reporting a security issue or attaching diagnostics.

Contributing

Contributions are welcome. Before opening a pull request:

pnpm install --frozen-lockfile
pnpm format:check
pnpm lint
pnpm typecheck
pnpm test
pnpm build
docker buildx build --load -t caldav-mcp:test .

Changes to CalDAV writes or iCalendar serialization must preserve ETag checks, opaque resource boundaries, unknown properties, recurrence exceptions, and alarms omitted from patches. TypeScript changes must continue to satisfy the rules in .codex/rules/typescript.md.

License

MIT. See LICENSE.