# WhatsApp Number Checker – Cal.com booking page

> Our WhatsApp number bulk checker API allows you to bulk check online if a phone number has an active WhatsApp account.

Booking page: https://cal.com/whatsapp-number-checker

## Event types

- [30 Min Meeting](https://cal.com/whatsapp-number-checker/30min): 30 min, confirmed instantly, event type id 2012923. Details: https://cal.com/whatsapp-number-checker/30min.md
- [15 Min Meeting](https://cal.com/whatsapp-number-checker/15min): 15 min, confirmed instantly, event type id 2012922. Details: https://cal.com/whatsapp-number-checker/15min.md

## Check availability

```http
GET https://api.cal.com/v2/slots?eventTypeId=<event type id>&start=YYYY-MM-DD&end=YYYY-MM-DD&timeZone=<IANA time zone>
cal-api-version: 2024-09-04
```

The response is `{"data":{"YYYY-MM-DD":[{"start":"<ISO 8601 with offset>"}]}}`; no API key is needed.

## Book

Each event type's `.md` document lists its required booking fields and the `POST https://api.cal.com/v2/bookings` request (`cal-api-version: 2026-02-25`).

## More

- API docs: https://cal.com/docs/api-reference/v2/introduction