CalDAV/ICS Sync

A self-hosted bidirectional synchronization service between CalDAV servers and ICS files. Manage multiple sync configurations through a web UI or REST API.

Built with Rust (Axum) backend and Next.js frontend. All configuration and data stored in SQLite.

Interface

Features

• CalDAV to ICS (Sources) -- Pull events from CalDAV servers and serve them as subscribable ICS endpoints
• ICS to CalDAV (Destinations) -- Push events from ICS files to CalDAV servers with configurable sync behavior
• Multi-source/destination management -- Add, edit, and delete configurations via the web UI or API
• Custom ICS paths -- Each source gets a user-defined URL path (e.g., /ics/work-calendar)
• Automatic background sync -- Per-source/destination configurable sync intervals
• Sync options -- Control whether to sync past events (sync_all) and whether to preserve local CalDAV events not in ICS (keep_local)
• Trailing slash compatibility -- Automatically retries CalDAV requests with toggled trailing slash for servers like Feishu/Nextcloud
• Password security -- Passwords are never returned in API responses; stored in plain text for CalDAV authentication. Sending an empty password on update preserves the existing value
• OpenAPI spec -- Full API documentation at /api/openapi.json
• Health checks -- /api/health and /api/health/detailed endpoints with live status in the UI
• Public ICS URLs - Optionally expose ICS feeds without authentication for Google Calendar and similar services
• Windows Fluent UI -- Dashboard styled with windows-ui-fabric for a native Windows look

Quick Start (Docker)

docker run -d \
  --name cal-sync \
  -p 6765:6765 \
  -v $(pwd)/data:/data \
  ghcr.io/robbyv2/caldav-ics-sync:latest

Open http://localhost:6765 to access the dashboard.

Docker Compose

services:
  cal-sync:
    image: ghcr.io/robbyv2/caldav-ics-sync:latest
    container_name: cal-sync
    ports:
      - '6765:6765'
    volumes:
      - ./data:/data
    # Optional: uncomment to enable HTTP Basic Auth on all routes.
    # Use AUTH_PASSWORD for plain text or AUTH_PASSWORD_HASH for argon2 (not both).
    # environment:
    #   - AUTH_USERNAME=admin
    #   - AUTH_PASSWORD=yourpassword
    #   # Or use a hashed password instead:
    #   # - AUTH_PASSWORD_HASH=$$argon2id$$v=19$$m=19456,t=2,p=1$$...
    restart: unless-stopped

Note

AUTH_USERNAME plus exactly one of AUTH_PASSWORD or AUTH_PASSWORD_HASH enables auth. Setting both password vars is an error. Generate a hash with: echo -n "yourpassword" | argon2 yoursalt -id -e

Important

When setting AUTH_PASSWORD_HASH via docker compose environment variables, you must escape each $ with another $ (or just pass in an env file)

Configuration

All sync configuration (sources, destinations, credentials) is managed through the web UI. The only environment variables are for server tuning:

Variable	Default	Description
SERVER_HOST	0.0.0.0	Bind address
SERVER_PORT	6765	Rust server port (user-facing)
PORT	6766	Next.js internal port
SERVER_PROXY_URL	http://localhost:6766	Internal proxy target
DATA_DIR	./data	Directory for SQLite database
DB_PATH	DATA_DIR/caldav-sync.db	Full path to SQLite database file
AUTH_USERNAME	(unset)	Basic Auth username (required to enable auth)
AUTH_PASSWORD	(unset)	Plain text password (mutually exclusive with hash)
AUTH_PASSWORD_HASH	(unset)	Argon2 PHC-format hash (mutually exclusive with above)

Concepts

Sources (CalDAV to ICS)

A source pulls events from a CalDAV server and exposes them as an ICS file at a custom path. Configure:

• CalDAV URL, username, and password
• ICS path (the URL path where the ICS file is served, e.g., /ics/my-calendar)
• Sync interval (seconds/minutes/hours, 0 for manual only)

Public ICS URLs

Sources can optionally make their ICS feed publicly accessible (without HTTP Basic Auth). Enable via the "Make ICS URL public" checkbox when creating or editing a source.

• With custom path: A dedicated URL at /ics/public/{custom-path} serves the feed without auth. The standard /ics/{path} still requires credentials.
• Without custom path (field left empty): The standard /ics/{path} URL becomes accessible without auth.

This is useful for services like Google Calendar that cannot supply HTTP Basic Auth credentials when subscribing to ICS feeds.

Destinations (ICS to CalDAV)

A destination downloads an ICS file from a URL and uploads each event to a CalDAV server. Inspired by ics_caldav_sync. Configure:

• ICS source URL (the remote ICS file to download)
• CalDAV server URL, calendar name, username, and password
• Sync interval (seconds/minutes/hours)
• sync_all -- whether to sync past events or only future ones
• keep_local -- whether to preserve CalDAV events that don't exist in the ICS file

API

The full OpenAPI spec is available at /api/openapi.json.

Sources

Method	Path	Description
GET	/api/sources	List all sources
POST	/api/sources	Create a source
PUT	/api/sources/:id	Update a source
DELETE	/api/sources/:id	Delete a source
POST	/api/sources/:id/sync	Trigger sync
GET	/api/sources/:id/status	Source status
GET	/ics/:path	Serve ICS file
GET	/ics/public/:path	Serve public ICS feed (no auth required)

Source Paths

Additional ICS/public paths per source, managed via API (not shown in the UI).

Method	Path	Description
GET	/api/sources/:id/paths	List paths for a source
POST	/api/sources/:id/paths	Add a path to a source
PUT	/api/sources/:id/paths/:path_id	Update a source path
DELETE	/api/sources/:id/paths/:path_id	Delete a source path

Each source path has a path (served at /ics/{path}) and an is_public flag. When is_public is true, the path is also accessible without authentication at /ics/public/{path}, and the standard /ics/{path} URL is auth-exempt. Paths are validated for uniqueness across all sources and source paths.

Destinations

Method	Path	Description
GET	/api/destinations	List all destinations
POST	/api/destinations	Create a destination
PUT	/api/destinations/:id	Update a destination
DELETE	/api/destinations/:id	Delete a destination
POST	/api/destinations/:id/sync	Trigger reverse sync

Health

Method	Path	Description
GET	/api/health	Health check
GET	/api/health/detailed	Detailed health

Local Development

All commands use just via the jfiles/ directory.

just src install    # Install dependencies
just src dev        # Run both servers (Rust + Next.js) with hot reload
just src fmt        # Format and lint all code
just src build-all  # Full production build
just src prod       # Build and run production

Navigate to http://127.0.0.1:6765.

Data Storage

All configuration and synced ICS data is stored in a single SQLite database. By default this is at DATA_DIR/caldav-sync.db, but can be overridden with the DB_PATH environment variable. Mount /data as a Docker volume for persistence.