---
title: Hidden fields
description: Capture extra information from your form link, like where the respondent came from, without asking for it.
icon: eye-off
search:
  keywords: [url parameters, utm, query string, tracking, source, ref, campaign]
---

Hidden fields save values from your form's link along with each response. Respondents never see them. Use them to track campaigns (`utm_source`), referrers (`ref`), or IDs from your own system (`customer_id`).

## Set up hidden fields

1. **Name your fields**

    Go to **Settings → General → Hidden fields** and enter the parameter names, separated by commas. For example: `utm_source, utm_campaign, customer_id`.

2. **Add them to your link**

    Add the values to your form link as URL parameters:

    ```text
    https://finerlise.com/f/your-form?utm_source=newsletter&customer_id=4821
    ```

3. **See them in your results**

    Each hidden field shows up as a column in your [submissions table](/responses/submissions-table), CSV exports, webhooks and integrations.

## Rules

- Up to **20** hidden fields per form.
- Names can use letters, numbers, `_`, `.` and `-`, up to 40 characters.
- Values can be up to 1,000 characters.
- `redirect_uri` and `state` are reserved for [Return to your website](/logic/return-to-your-website).

:::tip[Embedded forms] For [popups and widgets](/share/popup-forms), pass values with `data-finerlise-hidden-<name>` attributes, for example `data-finerlise-hidden-utm_source="homepage"`. For inline embeds, add the parameters to the embed URL. :::

:::note[Hidden fields aren't prefilled answers] Hidden fields store values but don't fill in visible questions. To prefill answers, use [Share links with prefill](/share/share-links-and-prefill). :::

**[Track UTM sources](/guides/track-utm-sources)**

See which campaign brings the most responses.

**[Respondent's country](/logic/respondents-country)**

Capture location automatically.