Mustdo MCP Server

mustdo-mcp

日本語版はこちら (README.ja.md)

MCP server for MustDo — the iOS To-Do alarm that keeps ringing until you do it.

It lets Claude (Claude Code, Claude Desktop, claude.ai, the Claude iPhone app) and any other Model Context Protocol client read and write your MustDo To-Dos.

• Your data stays in your iCloud. MustDo has no database of its own for To-Dos. They live in the CloudKit private database of your Apple ID (container iCloud.jp.lightning.mustdo, zone MustDo). This server talks to Apple's CloudKit Web Services and reads/writes the same records as the iPhone app.
• The developer never stores your To-Dos. Neither the local server in this repository nor the hosted relay (see below) keeps To-Do content on Lightning LLC servers.
• After a write, CloudKit pushes a silent notification to your iPhone, so the app updates right away.

Two ways to use it

A. Hosted relay — https://ltng.jp/api/mustdo/mcp

1. claude.ai → Settings → Connectors → Add custom connector → URL https://ltng.jp/api/mustdo/mcp (name it "MustDo").
2. Click Connect. You will see a consent page on ltng.jp explaining what is stored, then Apple's sign-in page. Sign in with the same Apple ID you use in the MustDo app.
3. Done. The same connector is available in the Claude iPhone app.

What the relay keeps, honestly:

• When you sign in, Apple issues a CloudKit sign-in token (ckWebAuthToken). The relay stores this token encrypted with AWS KMS (AWS Tokyo region) so it can call CloudKit on your behalf on each request.
• It also stores hashed OAuth access/refresh tokens for the connector itself.
• It does not store or log your To-Do content, your Apple ID email, your password, or your raw iCloud user ID.
• Disconnect: remove the connector in claude.ai and visit https://ltng.jp/api/mustdo/disconnect. After confirming with your Apple ID, the stored token is deleted immediately. It is also deleted automatically when Apple invalidates the sign-in (the tools then return RECONNECT_REQUIRED; just reconnect).

Full write-up: https://ltng.jp/mustdo/mcp.

B. Run locally (stdio)

Requirements:

• macOS with Node.js 24 or newer
• The MustDo app installed and synced to iCloud at least once (the app creates the zone and the Account record)
• A CloudKit API Token for the MustDo container. It is not currently distributed to the public — see "About the CloudKit API Token" below. Without it, use the hosted relay (A)

git clone https://github.com/lightning-llc-jpn/mustdo-mcp mustdo-mcp
cd mustdo-mcp
npm install
npm run build        # -> dist/index.js
npm test             # vitest; CloudKit is mocked

Register with Claude Code:

claude mcp add mustdo \
  -e MUSTDO_CK_API_TOKEN=<MUSTDO_CK_API_TOKEN> \
  -e MUSTDO_CK_ENV=production \
  -- node /path/to/mustdo-mcp/dist/index.js

Or put the settings in ~/.mustdo/config.json and register without -e:

{
  "apiToken": "<MUSTDO_CK_API_TOKEN>",
  "environment": "production"
}

Then ask Claude to run the sign_in tool once. The server opens Apple's sign-in page in your browser, listens on http://localhost:51234/callback, and saves the returned token to ~/.mustdo/auth.json (mode 0600).

About the CloudKit API Token

CloudKit Web Services needs two tokens on every request:

The API Token is container-wide and cannot be created by end users. Lightning LLC does not currently distribute it publicly, so running this server locally is not offered to general users — use the hosted relay (A). The code is published so that you can read exactly what the MCP server does with your data.

For reference, the token for the production environment has its Sign-in Callback set to https://ltng.jp/api/mustdo/oauth/local-callback, which simply redirects back to http://localhost:51234/callback without storing or logging anything.

Configuration

Environment variables win over ~/.mustdo/config.json.

auth.json is per environment; switching MUSTDO_CK_ENV requires another sign_in. Apple expires the session after a while (CloudKit returns HTTP 421); tools then return NOT_SIGNED_IN and you run sign_in again.

Tools

All tools return JSON. Dates in output are ISO 8601 (UTC). Dates in input may be:

• YYYY-MM-DD — that day at the account's default time (see below)
• YYYY-MM-DDTHH:mm — wall-clock time in the account's time zone
• Full ISO 8601 with offset

Default time and omitted due

Each account has a default alarm time (Account.defaultTime, HH:mm, set in the app's settings; 09:00 if unset).

• add_todo with no due → tomorrow (in the account's time zone) at the default time. Month/year boundaries and DST transitions follow the wall clock.
• due: "2026-10-10" → that day at the default time.
• get_me returns defaultTime and defaultDueNext so a client can tell the user when the alarm will ring.

Examples:

// "Remind me to buy milk" → tomorrow at the default time
{ "title": "Buy milk" }

// "Call the dentist on the 10th" → that day at the default time
{ "title": "Call the dentist", "due": "2026-10-10" }

// "Today at 3pm"
{ "title": "Submit report", "due": "2026-10-06T15:00" }

Repeat rules

Same vocabulary as the iOS Calendar app. Used as input to add_todo / update_todo and returned by list_todos.

{
  "kind": "none | daily | weekly | monthly | yearly",
  "interval": 1,                                   // 1 = every, 2 = every other … (1–99)
  "weekdays": [2, 4],                              // weekly only. 1 = Sun … 7 = Sat. Empty → weekday of `due`
  "monthly": { "mode": "dayOfMonth | weekdayOrdinal", "ordinal": 1, "weekday": 2 },
  "end": { "kind": "never | until | count", "until": "2026-12-31", "count": 10 }
}

Omitted fields take defaults (interval 1, weekdays [], monthly.mode dayOfMonth, end.kind never). Ranges: interval 1–99, ordinal 1–5 or -1, weekday 1–7, count 1–999. Anything else → INVALID_ARGUMENT. The legacy shape { "kind", "weekdays", "until" } is still accepted.

Expansion happens in the app, not here. list_todos returns the template plus occurrences (per-day done / skipped / snooze). Range filtering only drops templates that definitely cannot fire in range (first occurrence after the range, until before the range, weekly with no matching weekday).

Errors

Failures come back with isError: true and a body of { "code": "...", "message": "...", "details"?: {...} }.

Security model

• Access to your To-Dos is gated by your own Apple ID session (ckWebAuthToken), issued by Apple's sign-in page. No one — including the developer — can read your private database without it.
• The API Token only identifies the container and fixes where Apple may redirect after sign-in. Apple positions it as a client-side token (it is normally embedded in CloudKit JS web pages). By itself it grants no access to any user's private data.
• Locally, the session is stored in ~/.mustdo/auth.json (0600), logs go to stderr as JSON and never include tokens, and the sign-in listener binds to 127.0.0.1 / ::1 only.
• On the relay, the session is encrypted with AWS KMS per user (envelope encryption with encryption context), OAuth tokens are stored only as peppered SHA-256 hashes, PKCE S256 is mandatory, refresh tokens rotate with reuse detection, and To-Do content is never written to storage or logs.
• Writes use CloudKit recordChangeTag (optimistic locking) and retry once on conflict; deletes are soft.
• Anything you find: see SECURITY.md.

Development

npm install
npm run build       # tsc → dist/
npm test            # vitest (CloudKit mocked in test/fakeCloudKit.ts)
npm run typecheck   # tsc --noEmit
MUSTDO_LOG_LEVEL=DEBUG node dist/index.js   # run the stdio server by hand

Layout:

src/
  index.ts      entry point (stdio)
  server.ts     wiring for stdio: sign_in + the 7 To-Do tools
  tools.ts      tool definitions (zod schemas) shared by stdio and the relay
  core.ts       public entry for the shared core (no auth/config/stdio)
  service.ts    tool logic: filtering, upserts, conflict retry
  cloudkit.ts   thin CloudKit Web Services client (query / lookup / modify, 421 handling)
  records.ts    CloudKit record <-> model conversion
  dates.ts      time-zone-aware date math using Intl only
  auth.ts       auth.json and the sign-in callback listener
  config.ts     env / ~/.mustdo/config.json
  model.ts      enums, allowlists, RepeatRule types (mirrors the Swift app)
  errors.ts     ToolError / NotSignedInError
  log.ts        JSON logs to stderr (setLogSink to redirect)
test/           vitest

dist/core.js (package exports) is the shared core consumed by the hosted relay: everything except auth.ts, config.ts, index.ts and server.ts. Keep it free of anything that touches the local file system or a browser.

License

MIT — Copyright (c) 2026 Lightning LLC. See LICENSE.

MustDo is a product of Lightning LLC. Apple, iCloud and CloudKit are trademarks of Apple Inc.