synology-calendar-mcp

Claude Desktop extension that gives Claude access to the Calendar app of a Synology NAS — or to any other CalDAV server. List calendars, read events in a date range, create, change and delete appointments and todos, straight from a conversation. Ships as a single .mcpb file: install, fill in four fields, done.

Setup asks for a host name and a protocol switch, never a URL. The extension assembles the endpoint itself, which removes the single most common way to get CalDAV configuration wrong.

See also synology-contacts-mcp — the same idea for contacts over CardDAV — and github-mcp for repositories on github.com.

Features

• Events — list by date range, create, update, delete; all-day and recurring events included
• Todos — list (optionally filtered by status), create, update, complete, delete
• No URL to get right — host name plus an HTTPS switch; ports default to the DSM values 5001 (https) and 5000 (http)
• Forgiving input — a pasted https://, a trailing path or an explicit :port are handled instead of rejected
• Self-signed certificates — one switch, no manual NODE_TLS_REJECT_UNAUTHORIZED fiddling
• Runs locally — the server talks to your NAS directly; nothing is sent to a third party
• No credentials in the package — Claude Desktop stores the password in the OS keychain
• Nothing to install — Node ships with Claude Desktop, all dependencies are in the .mcpb

Requirements

• Claude Desktop 0.10.0 or newer (Windows, macOS, Linux)
• A reachable Synology NAS with the Calendar app installed and CalDAV enabled
• A DSM user account that owns the calendars

Installation

1. Grab synology-calendar-1.1.3.mcpb from Releases, or build it yourself (see below).
2. Claude Desktop → Settings → Extensions → Advanced settings → Install extension…, pick the file. Drag and drop onto the extensions window works too.
3. Fill in the fields (see next section) and enable the extension.
4. Ask Claude something like "which calendars do I have?".

Configuration

Field	Meaning
NAS-Adresse	Host name or IP only, e.g. nas.example.com. No https://, no path. A non-standard port goes here as nas.example.com:8443.
HTTPS verwenden	On → https, default port 5001. Off → http, default port 5000. These are the DSM defaults.
Benutzername	DSM login name of the user who owns the calendars
Passwort	DSM password; stored in the OS keychain, never in the package
Zertifikat prüfen	Leave off while the NAS uses its self-signed certificate. Turn on for a real certificate (e.g. Let's Encrypt).
Zeitlimit pro Anfrage	Seconds allowed per request, default 45. Leave it alone unless the NAS is slow enough to run into it.

The labels are German because the extension manifest is; the fields behave exactly as described above.

Tools

Tool	Purpose
list-calendars	All calendars with name and URL
list-events	Events in a date range
create-event	New event, optionally all-day or recurring
update-event	Change an existing event
delete-event	Remove an event
list-todos	Todos, optionally filtered by status
create-todo	New todo
update-todo	Change a todo
complete-todo	Mark a todo done
delete-todo	Remove a todo

How it works

1. Claude Desktop starts index.js with the configured fields as environment variables.
2. The wrapper builds CALDAV_BASE_URL from host name and protocol switch and appends the CalDAV path /caldav/. ts-caldav can find that path by itself on most servers, but not on DSM: its well-known probe uses GET where DSM only answers OPTIONS, and its fallback candidates carry no trailing slash where DSM insists on one. Discovery would fall back to the bare origin, DSM serves the web UI there, and no principal is ever found.
3. With certificate checking off, NODE_TLS_REJECT_UNAUTHORIZED=0 is set before anything connects.
4. The bundled caldav-mcp server takes over, exposes the ten tools over stdio and answers the MCP handshake immediately. The NAS is contacted on the first tool call, not at startup.

CALDAV_BASE_URL is still honoured if you set it directly, and wins over the host name — useful for a server that lives behind a path.

Environment variables

Useful if you want to run the server standalone rather than as an extension:

Variable	Meaning
CALDAV_HOST	Host name, :port optional
CALDAV_HTTPS	true (default) → https + port 5001, false → http + port 5000
CALDAV_USERNAME	DSM login name
CALDAV_PASSWORD	DSM password
CALDAV_VERIFY_SSL	false for a self-signed certificate
CALDAV_TIMEOUT	Seconds per request, default 45. Blank or unparsable falls back to the default.
CALDAV_BASE_URL	Legacy: a complete endpoint URL, wins over CALDAV_HOST

node index.js

Notes & caveats

• Shared calendars can be read-only. Synology hands out team calendars without write privileges in some configurations; writes then fail with HTTP 403.
• The connection is opened on first use, not at startup. A wrong password or an unreachable NAS therefore surfaces as an error on the tool that needed it, and the next call tries again. Up to and including 1.1.2 the server connected before it spoke MCP, so a NAS that stayed quiet for a minute cost the whole handshake and Claude Desktop reported "Verbindung zum Erweiterungs-Server nicht möglich" — an extension that looked broken while only the NAS was slow.
• Certificate checking off means exactly that. It disables TLS verification for the whole Node process. It is the right setting for a NAS with a self-signed certificate on your own LAN, and the wrong one over the open internet.
• The German field labels are not a bug, just the language the manifest was written in.
• DSM is slow to authenticate. The first authenticated request of a session regularly takes five seconds or more, later ones come from its session cache in milliseconds. ts-caldav hardcodes a 5000 ms timeout that caldav-mcp never overrides, so the wrapper raises it to 45 s before the server starts. The Zeitlimit pro Anfrage field changes that; it reaches the wrapper as CALDAV_TIMEOUT, in seconds, and a blank or unparsable value falls back to 45 rather than stopping the server. A NAS that needs several seconds per request on every call is worth looking at on the DSM side — a directory-service lookup running into its own timeout produces exactly that pattern.

Building the .mcpb yourself

npm install --prefix server --omit=dev
npx @anthropic-ai/mcpb pack . synology-calendar-1.1.3.mcpb

server/ holds the caldav-mcp package; only its node_modules are left out of this repository. Two files differ from upstream: server/dist/index.js builds the CalDAV client lazily instead of before the MCP handshake, and server/dist/tools/list-calendars.js fetches the calendar list per call instead of once at registration. Both changes are commented in place. To move to a newer caldav-mcp, replace the contents of server/, re-apply those two changes and bump the version in manifest.json.

Credits

Built around caldav-mcp by Dominik Grusemann (MIT), bundled with the two startup changes described under Building the .mcpb yourself.

Support this project ❤️

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License

This project is licensed under the MIT License — © 2026 Thomas Weirich.