proton-calendar-mcp

An MCP server for reading — and eventually modifying — a Proton Calendar.

Architecture

Proton Calendar has no public API and no CalDAV support, and event data is end-to-end encrypted. This server is built in phases:

• Phase 1 (working): reads via the calendar's secret ICS share link (Proton Calendar → Settings → Calendars → Share via link, "full view"). The feed is fetched on demand and cached for 60 seconds. Recurring events are expanded into concrete occurrences (RRULE, EXDATE, and overridden instances are honored).

• Phase 2 (planned): writes. See DEVELOPMENT.md once started.

Related MCP server: iCloud Calendar MCP

Tools

Setup

npm install
npm run build

Configure in your MCP client (e.g. claude_desktop_config.json):

{
  "mcpServers": {
    "proton-calendar": {
      "command": "node",
      "args": ["/path/to/proton-mcp/dist/index.js"],
      "env": {
        "PROTON_ICS_URL": "https://calendar.proton.me/api/calendar/v1/url/..."
      }
    }
  }
}

The ICS URL is a secret — anyone holding it can read the calendar. Keep it out of version control.

Development

npm run dev    # tsc --watch

Smoke test without an MCP client by piping JSON-RPC over stdin:

printf '%s\n' \
  '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"0"}}}' \
  '{"jsonrpc":"2.0","method":"notifications/initialized"}' \
  '{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"list_events","arguments":{}}}' \
  | PROTON_ICS_URL="..." node dist/index.js