Keeper.sh - Open-source calendar sync tool and universal calendar MCP server

Source
calendar-syncmcp-serverself-hosteddockeropen-sourcecaldavgoogle-calendaroutlook

Summary

Keeper.sh is an open-source calendar sync tool (AGPL-3.0) that pulls events from remote iCal/ICS sources and pushes them to one or more destination calendars (Google, Outlook, CalDAV, iCloud), solving the multi-calendar overlap problem. It also ships an MCP server that gives AI agents read-only access to calendar data via OAuth 2.1, making it directly useful for Claude Code/Claude Desktop integrations.

Key Insight

  • Solves a real pain point: when you have 3+ calendars (business, work, personal), meetings collide constantly. Keeper aggregates timeslots across all of them.
  • Key design choice: syncs timeslots only, not event details (titles, descriptions). If you need full detail sync, OneCal is the alternative.
  • MCP server exposes three tools: list_calendars, get_events (date range + timezone), get_event_count. Read-only, OAuth 2.1 authenticated.
  • Self-hosted Pro is completely free with all features (1-minute refresh, unlimited sources/destinations). Cloud Pro is 5 USD/month or 42 USD/year.
  • Standalone Docker image (keeper-standalone:2.9) bundles everything (web, API, cron, worker, Redis, PostgreSQL, Caddy) for dead-simple deployment.
  • Also supports granular deployment: separate images for each service, BYO Redis and PostgreSQL.
  • Sync logic is clean: push if no mapping exists, delete from destination if source event disappears, clean up orphaned Keeper-created events.
  • Events are tagged with @keeper.sh UID suffix (or a “keeper.sh” category on Outlook) for tracking.
  • SSRF protection available via BLOCK_PRIVATE_RESOLUTION flag with whitelist support for local CalDAV/ICS servers.
  • CLI, mobile, and SSH interfaces are listed as coming soon.