Google Calendar MCP Server

Fetch-native MCP server for listing calendars, searching and mutating events, responding to invitations, and checking Google Calendar availability. It runs on Bun and Cloudflare Workers and retains the project-specific Google OAuth proxy.

This repository targets the prerelease 2026-07-28 MCP candidate with @modelcontextprotocol/server@2.0.0-beta.5. It does not claim final conformance until the dated specification and stable packages are published and verified.

Tools

• list_calendars

• search_events

• check_availability

• create_event

• update_event

• delete_event

• respond_to_event

Existing all-calendar search, local substring matching, event-ID normalization, mutation fallback, free/busy behavior, Google Meet creation, and structured/natural-language event creation are preserved. Every tool advertises a complete Zod 4 input and output schema.

Related MCP server: mcp-google-calendar

Local setup

1. Enable Google Calendar API in Google Cloud.

2. Create a Web OAuth client.

3. Register http://127.0.0.1:3001/oauth/callback as a redirect URI.

4. Configure and start:

bun install
cp env.example .env
# Set PROVIDER_CLIENT_ID, PROVIDER_CLIENT_SECRET, and RS_TOKENS_ENC_KEY.
bun run dev

Local endpoints:

• MCP Resource Server: http://127.0.0.1:3000/mcp

• OAuth proxy: http://127.0.0.1:3001

Credential model

Three credentials remain separate:

1. MCP resource token — the opaque bearer token accepted by /mcp.

2. Google access token — resolved from storage, refreshed when necessary, and exposed to a fresh server only as AuthInfo.extra.providerAccessToken.

3. Google refresh token — remains encrypted in file/KV storage and never enters MCP tool context.

Tools never read or forward authInfo.token. Token-separation tests use visibly different MCP and Google tokens and assert that only the Google token reaches the provider mock.

OAuth proxy

The active proxy retains PKCE authorization, callback exchange, refresh, revocation, registration, redirect allowlists, and RS-to-Google token mappings.

Discovery endpoints:

• /.well-known/oauth-protected-resource/mcp

• /.well-known/oauth-authorization-server

Proxy endpoints:

• GET /authorize

• GET /oauth/callback

• POST /token

• POST /revoke

• POST /register

On Bun the proxy runs at OAUTH_ISSUER_URL (port 3001 by default). On Workers it is mounted outside /mcp on the same isolate.

Cloudflare Workers

Create KV and update its ID in wrangler.jsonc:

bun run kv:create
bun x wrangler secret put PROVIDER_CLIENT_ID --config wrangler.jsonc
bun x wrangler secret put PROVIDER_CLIENT_SECRET --config wrangler.jsonc
bun x wrangler secret put RS_TOKENS_ENC_KEY --config wrangler.jsonc
bun run deploy

Before deployment, set HTTPS values for MCP_PUBLIC_URL, OAUTH_ISSUER_URL, OAUTH_REDIRECT_URI, Host/Origin allowlists, and the Google redirect URI. RS_TOKENS_ENC_KEY must be a base64url-encoded 32-byte key.

Protocol and HTTP behavior

• One deployment-scoped fetch handler and a fresh McpServer per request

• Modern protocol pinned to candidate 2026-07-28

• SDK stateless fallback for legacy 2025-11-25 clients

• GET /mcp and DELETE /mcp return 405; no MCP session storage is used

• SDK-owned negotiation, header mismatch, cancellation, and transport errors

• Bounded MCP request bodies, strict Host/Origin checks, and allowlisted CORS headers

• Missing/invalid resource tokens return 401; missing Google scopes return 403

Validate

bun test
bun run typecheck
bun run lint
bun run format:check
bun run build
bun run build:worker
bun run types:worker:check

Provider tests use mocks. A live OAuth flow requires Google credentials, user consent, and redirect URIs configured in Google Cloud.

License

MIT