Connect WhatsApp to Cal.com — send booking reminders
Bridge Cal.com bookings to WhatsApp reminders via Google Calendar. Zellbox picks up every Cal.com booking and fires 24h + 2h WhatsApp reminders automatically.
by Nacho CollNacho founded Zellbox to give appointment-driven small businesses — clinics, salons, spas, physio, aesthetics, vets, mental-health, and fitness studios — a WhatsApp-first calendar and customer record system.
Editorial disclosure: I work at Zellbox. Cal.com steps described from their Google Calendar app docs as of August 2026.
Cal.com is the open-source scheduling primitive. Zellbox layers on the piece Cal.com doesn’t do: WhatsApp reminders. The bridge is your Google Calendar.
How it works
- In Cal.com → Apps → Google Calendar → install and pick as destination calendar.
- In Zellbox → Onboarding step 2 → connect the same Google Calendar.
- Every Cal.com booking now lands on your calendar. Zellbox fires WhatsApp reminders at 24 h and 2 h automatically.
What Zellbox adds beyond Cal.com’s built-in workflows
- WhatsApp reminders on top of Cal.com’s email + workflow-triggered SMS.
- Language-aware templates for multilingual customer bases.
- Signed consent PDFs — patients sign on their phone; PDF stored on the customer record.
- Two-way replies — customer responses land in your Zellbox inbox, not lost to the void.
Feature summary
| Zellbox layer | Cal.com built-in | |
|---|---|---|
| Booking + rescheduling | via Cal.com | Native + open-source |
| Email reminders | Not the focus | Native |
| Workflow-triggered SMS | Not the focus | Native (paid) |
| WhatsApp reminders | Native + free tier | Not available |
| Signed consent PDFs | Native | Not available |
Setup ~10 minutes end-to-end — no BSP contract, no code.
About the author: Nacho Coll is the founder of Zellbox. He writes about WhatsApp Business automation for appointment-driven small businesses.
Frequently asked questions
How does Cal.com connect to WhatsApp via Zellbox?
Is this available on Cal.com's free tier?
Does the reminder respect the guest's language?
About the author
Nacho Coll
Founder & Engineer at Zellbox
Nacho founded Zellbox to give appointment-driven small businesses — clinics, salons, spas, physio, aesthetics, vets, mental-health, and fitness studios — a WhatsApp-first calendar and customer record system. Writes about WhatsApp Business automation, no-show economics, recall-cycle playbooks, and the operational realities of running visit-driven businesses at scale.
