Google Calendar Streamable

This server is a remote Model Context Protocol (MCP) server for Google Calendar. A model can use it to list calendars, find events, check free and busy times, create, change, move and delete events, and answer invitations. The server runs on Cloudflare Workers and on Bun. It uses the MCP server template 2.1 and the official MCP TypeScript SDK 2.3.0.

The server URL is the deployed Worker's MCP_PUBLIC_URL, for example https://google-calendar.<subdomain>.workers.dev/mcp.

The server uses protocol version 2026-07-28. It also accepts clients that use the 2025 protocol versions.

[!WARNING] You connect this server to your MCP client at your own risk. A model can make mistakes. Examine what the tools do, and examine the changes in your calendar. The tools can delete events and can send updates to attendees.

Tools

Tool	Function
list_calendars	Lists the calendars of the user, with their IDs, access roles and time zones.
search_events	Finds events in all readable calendars (the default), in one calendar, or in a list of calendars. It filters by time range, text and event type. The text match is a substring match on the title, description, location and attendees.
check_availability	Shows the busy times of one or more calendars in a time range.
create_event	Makes an event from a sentence (Google's quick add) or from fields: title, start, end, attendees, Google Meet, recurrence, reminders.
update_event	Changes the given fields of an event. It can also move the event to another calendar.
delete_event	Deletes an event.
respond_to_event	Sets the user's answer to an invitation: accepted, declined or tentative.

By default, create_event, update_event and delete_event send no notification to attendees (sendUpdates: none). respond_to_event notifies everyone (sendUpdates: all). If Google cannot find an event under the owner's email address, the server tries again with primary.

Connect a client

Use the server URL and the Streamable HTTP transport. The client signs you in with Google the first time.

Client	Procedure
Claude	In Settings → Connectors, add a custom connector with the server URL.
Claude Code	Run claude mcp add --transport http google-calendar <server URL>.
MCP Inspector	Run bun run inspector. Select Streamable HTTP. Enter the server URL.

Alice and Wonderlands use the same URL.

Authentication

The server is its own OAuth authorization server, in front of Google's OAuth. MCP clients do not receive Google tokens.

1. The client registers at /register and signs the user in at /authorize. The client must use PKCE S256.
2. The server sends the user to Google. Google asks for the two Calendar scopes.
3. Google returns the user to the server's /oauth/callback. The server keeps the Google tokens, encrypted.
4. The client gets a code, and exchanges the code at /token for an access token and a refresh token. These tokens are opaque and have meaning only for this server.
5. On each MCP request, the server finds the Google token for the access token. If the Google token expires in less than one minute, the server refreshes it first. The tools use the Google token. They do not see the client's token.

For the complete flow, the storage and the redirect rules, refer to docs/oauth.md.

Configuration

The deployment settings are in wrangler.production.jsonc (Workers; gitignored, with wrangler.production.example.jsonc as its shape) or .env (Bun). .env.example describes all variables.

Variable	Production value	Function
MCP_PUBLIC_URL	https://google-calendar.<subdomain>.workers.dev/mcp	The public URL of the MCP endpoint. It is also the resource that tokens are issued for.
MCP_ALLOWED_HOSTS	google-calendar.<subdomain>.workers.dev	The Host headers that the server accepts.
MCP_ALLOWED_ORIGIN_HOSTNAMES	The server host, claude.ai, claude.com, and the hosts of the operator's own browser clients	The browser origins that the server accepts.
AUTH_MODE	oauth	The server checks the tokens that it issued.
OAUTH_ISSUER_URL, OAUTH_AUTHORIZATION_URL, OAUTH_TOKEN_URL, OAUTH_REGISTRATION_URL	This server's origin, /authorize, /token and /register	The authorization server that clients use. The server does not start if they name another server.
OAUTH_SCOPES	The two Calendar scopes	The scopes that every MCP request must have.
PROXY_REDIRECT_ALLOWLIST	The callbacks of Alice, Claude and the operator's other clients	The client redirect URIs that the proxy accepts, in addition to native loopback URIs.
MCP_MAX_REQUEST_BYTES	1048576	The largest MCP request body.
MCP_LEGACY_MODE	stateless	The server also accepts 2025-era clients.

Secrets:

Secret	Function
PROVIDER_CLIENT_ID	The server's Google OAuth client ID.
PROVIDER_CLIENT_SECRET	The server's Google OAuth client secret.
TOKENS_ENC_KEY	32 random bytes, base64url. The key encrypts the stored tokens. If you change it, all users must sign in again.

In production, the server does not start without these three secrets. The Google endpoints, the Calendar scopes and the offline-access parameters are constants in src/services/google-oauth.ts. For the setup at Google and at Cloudflare, refer to docs/deploy.md.

Development

Requirements: Bun 1.4 or later, and Node.js 22.18 or later.

1. Install the dependencies:

   bun install
   

2. Copy .env.example to .env. Set PROVIDER_CLIENT_ID, PROVIDER_CLIENT_SECRET and TOKENS_ENC_KEY. At Google, allow the redirect URI http://127.0.0.1:3000/oauth/callback.

3. Start the server:

   bun run dev
   

   The server URL is http://127.0.0.1:3000/mcp. To use the Cloudflare local runtime, run bun run dev:worker (port 8787). Put its secrets in .dev.vars.

4. Before you commit, run the checks:

   bun run check
   bun run test:smoke
   

bun run check does the type check, the lint check and the tests. bun run test:smoke starts the real server on Bun and on workerd. It signs in through a Google stand-in on loopback and calls the tools. No test uses the network.

Script	Function
bun run dev	Starts the server on Bun.
bun run dev:worker	Starts the server in the Cloudflare local runtime.
bun run check	Type check, lint check, tests, and the check of the generated Worker types.
bun run test:smoke	Smoke tests on Bun and on workerd.
bun run deploy	Deploys with the gitignored wrangler.production.jsonc (wrangler deploy --config wrangler.production.jsonc).
bun run types:worker	Makes the Worker types again after a change to wrangler.jsonc.

Project structure

src/
  server.ts       Identity, Runtime, Deps, and the hooks that connect the OAuth proxy
  settings.ts     The Google client, the encryption key, the redirect allowlist
  tools/          One file for each tool; shared/ has schemas and helpers
  services/       The Google Calendar API client, and google-oauth.ts: Google as the OAuth provider
  oauth/          The OAuth proxy. It is the same for every provider (docs/oauth.md)
  platform/       Template code. Do not change it
  bun.ts          Entry point for Bun: file storage
  worker.ts       Entry point for Workers: KV and the NativeOAuthAuthority Durable Object
tests/            Tests for the tools, the proxy and the platform; fixtures from before 1.1.0
scripts/          Smoke tests and the Google stand-in

For the template's concepts (the request path, defineTool, the error policy, the configuration checks), refer to the template documentation.

License

MIT