# Build Better: a 30-minute call with Justin with Justin · Just Build Better

> A focused conversation about the idea, product, or process you want to improve. We’ll find the most useful next step together.

- Host: Justin · Just Build Better
- Duration: 30 min
- Location: Cal Video
- Host time zone: America/Phoenix
- Confirmation: Bookings are confirmed instantly.
- Booking page: https://cal.com/justbuildbetter/talk
- Event type id: 7231360

## Check availability

```http
GET https://api.cal.com/v2/slots?eventTypeId=7231360&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": 7231360,
  "start": "<UTC ISO 8601 start from the slots response>",
  "attendee": {
    "name": "…",
    "email": "…",
    "timeZone": "<IANA time zone>"
  },
  "bookingFieldsResponses": {
    "attendeePhoneNumber": "…",
    "notes": "…"
  }
}
```

- Required fields: `name` (Your name), `email` (Email address)
- Optional fields: `attendeePhoneNumber` (Best number for Justin to call), `notes` (What are you building better?)
- `name` and `email` go in `attendee` and `guests` is a list of emails; every other field goes in `bookingFieldsResponses` under its name.