Holiday Sync — Google Calendar Add-on Template (Apps Script)

A fully-built Google Calendar add-on template that lets you sync global holidays with reminders, color-coding, and yearly auto-refresh. 100% editable Apps Script. No backend required.

Holiday Sync is a complete Google Apps Script + CardService project that works as a native Google Calendar add-on. It allows users to:

• Select from multiple holiday categories (Christian, Jewish)
• Auto-sync chosen holidays to Google Calendar
• Avoid duplicates with built-in duplicate protection
• Apply color coding for different holiday groups
• Set reminder hours for all synced events
• Trigger yearly refresh automatically (time-based triggers included)
• Store user settings via PropertiesService
• Send optional email notifications
• Use a clean, multi-step CardService UI inside Google Calendar

Completely serverless. Runs entirely inside Google Apps Script.

WHO THIS IS FOR

• Developers building productivity tools
• SaaS founders building Workspace add-ons
• Agencies wanting custom calendar automation
• Freelancers wanting a deploy-ready script
• Anyone wanting to publish a Google Calendar add-on
• Non-developers who want holiday reminders without subscriptions

WHAT’S INCLUDED

• Full Google Apps Script source code (.ZIP)
• Full CardService UI flow with onboarding, settings, and update cards
• Complete holiday datasets (Christian, Jewish)
• Yearly refresh trigger
• Reminder logic with custom hours
• Duplicate-safe event creation
• Color coding support
• Email notifications via MailApp
• Fully commented source code

ALSO INCLUDED

• Step-by-step Installation Guide (PDF)
• Step-by-step Deployment Guide to create your own private add-on
• Instructions to add more holidays
• Instructions to add premium features (if you want to resell)
• Complete OAuth scopes list already configured

WHAT YOU CAN DO WITH IT

• Use it personally on your own Google Calendar
• Deploy a private add-on for your business or clients
• Customize and rebrand it
• Extend with more countries, religions, or custom dates
• Integrate with workflows (API, Sheets, CRM, etc.)
• Sell your own edition of the add-on (license included)

WHAT YOU CANNOT DO

• Resell this exact template as-is on Gumroad
• Claim exclusive ownership of the underlying code structure
• Publish it to the Google Workspace Marketplace without doing Google’s verification steps

WHY THIS IS VALUABLE

Google Calendar does not allow HTML or custom web apps inside add-ons.
Building a Calendar add-on with CardService is non-obvious and time-consuming.

This template saves:

• 20–40 hours of UI building
• 10–20 hours of Calendar API edge-case handling
• 10–15 hours of trigger, OAuth, and deployment setup
• Weeks of trial-and-error if you’re new to Workspace add-ons

This is production-ready, not a beginner tutorial.

BONUS FEATURES

• Clean onboarding wizard
• Professional card layout
• Dynamic holiday selection
• Storage of user preferences
• Fully modular code structure
• Built-in extension hooks for premium add-ons

SUPPORT

If you run into any issues during setup or customization, you can contact us directly on Gumroad, and we will assist.