# 15-minute product design call with Kaspar Kuus

> Have a product idea, mobile journey or design challenge you want to make clearer? In 15 minutes, we’ll discuss what you are building, what feels stuck and whether working together makes sense. You’ll leave with a practical next step.

- Host: Kaspar Kuus
- Duration: 15 min
- Location: Cal Video
- Host time zone: Europe/Tallinn
- Confirmation: Bookings are confirmed instantly.
- Booking page: https://cal.com/kasparkuus/15min
- Event type id: 6334131

## Check availability

```http
GET https://api.cal.com/v2/slots?eventTypeId=6334131&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

```http
POST https://api.cal.com/v2/bookings
cal-api-version: 2026-02-25
Content-Type: application/json

{
  "eventTypeId": 6334131,
  "start": "<UTC ISO 8601 start from the slots response>",
  "attendee": {
    "name": "…",
    "email": "…",
    "timeZone": "<IANA time zone>"
  },
  "guests": [
    "guest@example.com"
  ],
  "bookingFieldsResponses": {
    "notes": "…"
  }
}
```

- Required fields: `name` (Your name), `email` (Email address)
- Optional fields: `notes` (Additional notes), `guests` (Add guests)
- `name` and `email` go in `attendee` and `guests` is a list of emails; every other field goes in `bookingFieldsResponses` under its name.