CalIn — ICS Calendar to Exchange Sync

---

name: calin

description: Sync any ICS/iCal calendar to Microsoft Exchange as blocked time slots — supports recurring events, change detection, and privacy-preserving sync

version: 1.0.0

metadata:

clawdbot:

os: ["darwin"]

requires:

env:

- CALINT_ICS_URL

- CALINT_MS_CLIENT_ID

- CALINT_MS_TENANT_ID

bins:

- python3

config:

- ~/.calintegration/.env

primaryEnv: CALINT_ICS_URL

files: ["*.py", "install.sh", "requirements.txt"]

homepage: https://github.com/Blucaru/CalIn

---

# CalIn — ICS Calendar to Exchange Sync

Sync busy time from **any ICS/iCal calendar** to Microsoft Exchange as "Blocked" slots. Works with Google Calendar, iCloud, Outlook.com, Nextcloud, Fastmail, Proton Calendar, or any CalDAV server that publishes an ICS feed.

When to Use This Skill

What It Does

Setup

1. Install dependencies

Requires Python 3.12+.

cd ~/.openclaw/skills/calin
bash install.sh

This creates a Python venv and installs `icalendar`, `msal`, `recurring-ical-events`, and `requests`.

2. Configure credentials

Add to `~/.calintegration/.env` (created by installer with chmod 600):

CALINT_ICS_URL=<your-ics-feed-url>
CALINT_MS_CLIENT_ID=<azure-app-client-id>
CALINT_MS_TENANT_ID=<azure-app-tenant-id>
# Optional: sync to a specific Exchange calendar (defaults to primary)
# CALINT_MS_CALENDAR_ID=<calendar-id>

**Where to find your ICS URL:**

| Provider | Location |

|----------|----------|

| Google Calendar | Settings > your calendar > Integrate > "Secret address in iCal format" |

| iCloud | Calendar app > right-click calendar > Share > Public Calendar > copy URL |

| Outlook.com | Settings > Calendar > Shared calendars > Publish > ICS link |

| Nextcloud | Calendar > three-dot menu > Copy subscription link |

| Fastmail | Settings > Calendars > Share/export > ICS URL |

**Azure AD app** (free, no client secret needed):

1. Go to https://portal.azure.com/#view/Microsoft_AAD_RegisteredApps/ApplicationsListBlade

2. New registration > Name: "CalIn" > Redirect URI: Public client > `http://localhost:8400`

3. API permissions > Add > Microsoft Graph > Delegated > Calendars.ReadWrite

4. Copy Application (client) ID and Directory (tenant) ID

3. Authenticate Microsoft

cd ~/.openclaw/skills/calin
venv/bin/python main.py setup

This opens a browser for one-time Microsoft login. Tokens are cached locally.

Commands

Run these from the skill directory:

| Command | What it does |

|---------|-------------|

| `venv/bin/python main.py sync` | Run one sync cycle |

| `venv/bin/python main.py status` | Show last sync time and event count |

| `venv/bin/python main.py clear` | Remove all synced events from Exchange |

| `venv/bin/python main.py setup` | Re-run authentication setup |

Automated Sync (macOS)

The installer generates a launchd plist for automatic sync every 5 minutes:

cd ~/.openclaw/skills/calin
bash install.sh
cp com.calintegration.sync.plist ~/Library/LaunchAgents/
launchctl load ~/Library/LaunchAgents/com.calintegration.sync.plist

How It Works

1. Fetches the ICS feed and expands all recurring events within a 14-day window

2. Compares against the local event map (previous sync state)

3. For each event:

- **New**: Creates a "Blocked" event on Exchange

- **Changed** (time moved): Updates the Exchange event

- **Deleted** from source: Deletes the Exchange event

4. Saves updated event map and last sync timestamp

Change detection uses a hash of start time + end time + all-day flag. Only changed events trigger API calls.

Security and Privacy

External endpoints called

| Endpoint | Purpose | Auth |

|----------|---------|------|

| Your ICS URL (HTTPS) | Read calendar events | URL contains secret token |

| `login.microsoftonline.com` | Microsoft OAuth token exchange | PKCE flow |

| `graph.microsoft.com/v1.0` | Create/update/delete Exchange events | Bearer token |

Data flow

ICS Feed (read-only) --> [CalIn on your machine] --> Microsoft Graph API (write)
                              |
                     ~/.calintegration/ (local state)

No data is sent to any third party. All processing happens locally.