Calendar Sync

A Cloudflare Worker that syncs your Outlook calendar to Google Calendar every minute using an ICS feed.

I got tired of manually checking two calendars and didn't want to pay $20 subscription for a subscription service to do it. This runs on Cloudflare's free tier and costs essentially nothing.

Read the full write-up on my blog: Calendar Sync

This could run on any serverless platform (Vercel, AWS Lambda, Deno Deploy, etc.) but I went with Cloudflare Workers.

What it does

• Fetches your Outlook calendar via its public ICS link
• Creates/updates/deletes events in a Google Calendar to match
• Runs every minute
• Tracks synced events so it won't duplicate or lose changes

Limitations

• One-way sync only (Outlook → Google)
• No attendee info (Outlook's ICS feed strips this for privacy)
• Events sync within a window of -30 days to +1 year

Setup

1. Get your Outlook ICS URL

1. Go to Outlook → Settings → Calendar → Shared calendars
2. Under "Publish a calendar", select your calendar and publish it
3. Copy the ICS link

2. Set up Google Cloud

1. Go to Google Cloud Console
2. Create a project
3. Enable the Google Calendar API
4. Go to APIs & Services → OAuth consent screen
   • Set up as External
   • Add scope: https://www.googleapis.com/auth/calendar
   • Add yourself as a test user
5. Go to APIs & Services → Credentials
   • Create an OAuth 2.0 Client ID (Web application)
   • Add http://localhost:3000/callback as an authorized redirect URI
   • Copy the Client ID and Client Secret

3. Create a destination calendar in Google

1. In Google Calendar, create a new calendar (e.g., "Work")
2. Go to its settings → Integrate calendar → Copy the Calendar ID

4. Configure and deploy

# Clone and install
git clone <repo-url>
cd calendar-sync
npm install

# Add your credentials to .env
cp .env.example .env
# Edit .env with your values (ICS URL, Google Client ID, Secret, Calendar ID)

# Get your Google refresh token
npm run auth

# Add the refresh token to .env
# Generate a random token for SYNC_TOKEN (e.g., openssl rand -hex 32)

# Deploy secrets to Cloudflare
npx wrangler secret put OUTLOOK_ICS_URL
npx wrangler secret put GOOGLE_CLIENT_ID
npx wrangler secret put GOOGLE_CLIENT_SECRET
npx wrangler secret put GOOGLE_REFRESH_TOKEN
npx wrangler secret put GOOGLE_CALENDAR_ID
npx wrangler secret put SYNC_TOKEN

# Deploy
npm run deploy

5. Test

Trigger a manual sync (token required):

curl "https://your-worker.workers.dev/sync?token=YOUR_SYNC_TOKEN"

Logs

View real-time logs:

npx wrangler tail

License

MIT