CalDAV Forwarder

A completely stateless Model Context Protocol server that forwards calendar operations to a CalDAV server from Cloudflare Workers.

Source code and deployment guidance are available in the GitHub repository.

Status: Functional first release. The Worker supports calendar discovery, event listing/search, event retrieval, creation, updates, deletion, and free/busy queries.

Connect in three steps

1. Open https://caldavmcp.anpc.work in a browser.
2. Enter your CalDAV server, username, and app password, then click Test connection. Leave Calendar URL blank to discover calendars automatically.
3. Choose a default calendar if desired, create the secure token, then copy the generated MCP URL or configuration into your AI assistant.

The public page creates encrypted tokens with no expiration by default for a set-and-forget connection. You can optionally choose a shorter lifetime. Credentials are sent over HTTPS to the Worker for encryption and are never decoded in the browser. Rotate CONNECTION_TOKEN_KEY if tokens need to be revoked.

The assistant can list, search, read, create, update, and delete events, and query free/busy information. Every request is independent; no calendars, credentials, or sessions are stored.

Security model

Do not place raw passwords, app passwords, or access tokens directly in a URL. URLs may be retained by browser history, reverse proxies, analytics systems, and access logs.

Connection tokens are encrypted AES-GCM values:

POST https://caldavmcp.anpc.work/mcp/<encrypted-connection-token>

The token represents connection details such as:

{
  "serverUrl": "https://caldav.example.com",
  "calendarUrl": "https://caldav.example.com/calendars/user/work/",
  "username": "[email protected]",
  "password": "app-password",
  "expiresAt": 1797700000
}

The Worker decrypts each token for one request and discards the connection details afterward. Tokens do not expire unless an expiration is selected when creating them; rotate CONNECTION_TOKEN_KEY to revoke all tokens created with the previous key. Event and free/busy URLs must belong to the configured CalDAV server. Configure it as a Worker secret. The key must be URL-safe base64 containing a 128-, 192-, or 256-bit AES key.

Prefer provider-specific app passwords or OAuth access tokens over a primary account password. Never commit tokens or credentials to this repository.

Connecting an MCP client

After deploying the Worker, configure your MCP client with the Worker URL. The exact configuration varies by client, but the endpoint is:

https://caldavmcp.anpc.work/mcp/<encrypted-connection-token>

For an MCP client configuration that accepts a remote HTTP server, use the endpoint as the server URL. For example:

{
  "mcpServers": {
    "caldav": {
      "type": "http",
      "url": "https://caldavmcp.anpc.work/mcp/<encrypted-connection-token>"
    }
  }
}

Do not paste the example token above into a real client. Replace it with a token generated for the intended CalDAV account and calendar.

The assistant will be able to call tools such as:

• list_calendars
• list_events
• search_events
• get_event
• create_event
• update_event
• delete_event

Example requests an assistant could handle:

• “What is on my work calendar tomorrow?”
• “Create a dentist appointment next Tuesday at 10:00.”
• “Move my 3 PM meeting to Friday.”
• “Cancel the event titled ‘Project review’.”
• “Find all events mentioning the quarterly planning meeting.”

The assistant should confirm important destructive actions, especially event deletion, before calling the corresponding tool.

Tool output format

Tool responses use compact JSON with only information needed for the next action:

• Calendar lists contain url, plus available displayName, description, timezone, and color.
• Event lists and get_event contain url, optional etag, and the current iCalendar data.
• create_event returns the created event url.
• update_event returns the updated event url.
• delete_event returns the deleted event url and deleted: true.
• get_free_busy returns only the free/busy iCalendar data.

Responses do not include HTTP status codes, raw CalDAV metadata, or presentation formatting.

Deployment

Install dependencies:

npm install

Run the Worker locally:

npm run dev

Type-check the project:

npm run typecheck

Run unit tests

npm test

Run tests with coverage

npm run coverage

Coverage thresholds are enforced at 90% for statements, lines, and functions, and 85% for branches. The current unit-testable source modules report 100% in all four categories. The Cloudflare Worker entrypoint is excluded because it requires the Workers runtime and external CalDAV services; validate it with a deployed or wrangler dev smoke test.

Deploy to Cloudflare Workers:

npx wrangler login
npm run deploy

The Worker is configured as a Cloudflare Custom Domain at caldavmcp.anpc.work. Wrangler creates the domain and certificate when the zone is active in the same Cloudflare account. Set the required secret before deploying:

npx wrangler secret put CONNECTION_TOKEN_KEY
npm run deploy

The domain must be active in Cloudflare DNS. Do not add a conflicting CNAME record for caldavmcp.anpc.work; Custom Domains manage the DNS record.

Set the encryption key as a Cloudflare Worker secret:

npx wrangler secret put CONNECTION_TOKEN_KEY

For local development, create .dev.vars from .dev.vars.example and replace the placeholder with a generated key. Wrangler loads .dev.vars automatically when running npm run dev; do not commit that file.

cp .dev.vars.example .dev.vars
openssl rand -base64 32 | tr '+/' '-_' | tr -d '='

Never put the encryption key in wrangler.jsonc, source code, or client configuration.

Available tools

All tools operate on the calendar selected by calendarUrl in the token, or accept an explicit calendarUrl where appropriate.

Tool	Purpose
list_calendars	Discover calendars in the account.
list_events	List events for a required start/end range. Without calendarUrl, searches all calendars.
search_events	Search event data by text. Without calendarUrl, searches all calendars.
get_event	Fetch an event by its object URL.
create_event	Create an event with summary, start, and end.
update_event	Update an event using its current iCalendar data and object URL.
delete_event	Delete an event, optionally supplying its ETag.
get_free_busy	Query free/busy data for a time range.

Dates should be ISO 8601 strings, for example 2026-08-20T10:00:00Z. Event updates require the current iCalendar data so unknown provider-specific properties are preserved.

Tool behavior for agents

• Call list_calendars first when the available calendar URLs are unknown.
• list_events and search_events require start and end. An explicit calendarUrl selects one calendar. Without it, the token's configured calendar is used; if none is configured, all calendars are searched.
• search_events performs a case-insensitive text search over each event's iCalendar data, not only the event title.
• get_event requires the event's current HTTPS object URL.
• create_event requires summary, start, and end; calendar selection is explicit URL, token calendar, then the first available calendar.
• update_event requires the current event data; send only fields that should change because omitted fields are preserved.
• delete_event permanently removes an event. Confirm the deletion with the user first, and pass the current ETag when available.
• get_free_busy returns iCalendar free/busy data for the requested range and does not list event details.

Stateless request flow

MCP client
   |
   | POST /mcp/<encrypted-token>
   v
Cloudflare Worker
   | decrypt token in memory
   | create request-scoped CalDAV client
   | perform one operation
   | discard credentials and response data
   v
CalDAV server

No calendar data or MCP session state is retained by this Worker. The request body, credentials, and CalDAV response exist only during the request.

Provider notes

CalDAV implementations differ. You may need an app password or provider-specific endpoint:

• Nextcloud: usually supports app passwords and calendar collection URLs.
• Fastmail: use an app-specific password and the CalDAV endpoint provided by Fastmail.
• iCloud: generally requires an app-specific password and the account’s CalDAV endpoint.
• Google Calendar: native CalDAV support is limited; use Google’s API instead if CalDAV compatibility is insufficient.

Always test calendar discovery, recurring events, time zones, attendees, ETags, and deletion behavior with the target provider.

Technology

• Cloudflare Workers
• TypeScript
• @modelcontextprotocol/sdk
• tsdav
• ical.js
• zod

Limitations

The service forwards requests and does not become a calendar synchronization service. It does not maintain a local event index, deduplicate events across calendars, or queue work for later execution. If a CalDAV provider is unavailable, the request fails without being retried from persistent storage.