# Keeper.sh: open-source calendar sync and calendar MCP server

> Keeper.sh syncs timeslots across multiple calendars and ships an MCP server giving AI agents read-only calendar access via OAuth 2.1.

Published: 2026-03-25
URL: https://daniliants.com/insights/keeper-sh-open-source-calendar-sync-tool-and-universal-calendar-mcp/
Tags: calendar-sync, mcp-server, self-hosted, docker, open-source, caldav, google-calendar, outlook

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## 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.