> ## Knowledge Base Index
> Fetch the complete knowledge base index at: https://help.cal.id/sitemap.xml
> Use this file to discover available pages before exploring further.
> Pure-Markdown content can be obtained by appending a '.md' suffix to the content URLs listed in the sitemap (without the trailing slash).

# How to Hide and Prefill Booking Questions?

In **Cal ID**, prefill what you already know and hide fields meant only for internal tracking (referral source, Lead IDs) — keeping your form short while capturing useful data.

| 1. Add the question

1. Open **Event Types** and click **Edit** on the event.
2. Open the **Advanced** tab and, in **Booking questions**, click **+ Add a question**.

![](https://storage.crisp.chat/users/helpdesk/website/-/6/f/1/c/6f1c2c7b8034d000/image_1qeob0b.png =1151x615)

3. Set the **Label** (e.g., "Referral Source") and note the **Identifier** (e.g., `referral`) — you'll need it exactly to prefill later. Click **Add**.

![](https://storage.crisp.chat/users/helpdesk/website/-/6/f/1/c/6f1c2c7b8034d000/image_op2hlp.png =1168x615)

| 2. Hide the question

To record a field in your calendar but hide it from the guest:

1. Toggle the question to **Hidden**.

![](https://storage.crisp.chat/users/helpdesk/website/-/6/f/1/c/6f1c2c7b8034d000/image_1yjsf11.png =1154x615)

2. Optionally click **Edit** and tick **"Disable input if the URL identifier is prefilled"** so guests can't change a prefilled value.

![](https://storage.crisp.chat/users/helpdesk/website/-/6/f/1/c/6f1c2c7b8034d000/image_udqk0z.png =1167x615)

3. Click **Save**.

| 3. Prefill via URL

Append a query parameter matching the question's **Identifier**: `URL?identifier=value` (use `?` for the first parameter, `&` for more).

![](https://storage.crisp.chat/users/helpdesk/website/-/6/f/1/c/6f1c2c7b8034d000/image_dzd7ql.png =1213x615)

**Example:** identifier `referral`, value `Instagram` →
`https://cal.id/username/eventtype?referral=Instagram`

If the URL already has parameters, chain with `&`:
`https://cal.id/username/eventtype?overlayCalendar=true&referral=Instagram`

| Why this helps

* **Data integrity:** a hidden question still records its value (e.g., "Referral: Instagram") in your calendar and dashboard.
* **Personalization:** send partners their own prefilled links to see who drives bookings.
* **Clean forms:** capture campaign or user IDs behind the scenes.