> For the complete documentation index, see [llms.txt](https://docs.dapta.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.dapta.ai/dapta-forms/builder/hidden-fields-and-url-prefill.md).

# Hidden fields & URL prefill

Prefill any Dapta Forms question from the link with ?key=value, hide a question so it is filled only from the URL, copy the ready-made example from the Prefill from URL block, and understand precedenc

Every question in a form can be filled from the link that opens it. Add `?key=value` to the public URL and the answer arrives already typed in. Turn on **Hidden question** and the respondent never sees the question at all: the value from the link is stored with their submission, which is the easy way to pass a promo code, a campaign name or a lead source from your ads, emails or CRM into the form.

***

**Step 1:** In the editor, select a question and open **Advanced settings** in the **Question settings** pane. The first block is **Prefill from URL**. It is read only and shows your real public link with a sample value for this question, for example `/k7m2xq/alex/lead-qualification-quiz?company=value`. Click **Copy** to copy it.

<figure><img src="https://3835013762-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FCy5rSNtQmtqYCGzJlNEB%2Fuploads%2Fgit-blob-330d4c75c885e81fb52acf2659ad4f4b45237d54%2Fforms-hidden-fields-and-url-prefill-01-prefill-block.png?alt=media" alt="The Prefill from URL block under Advanced settings showing the public link with ?company=value and a Copy button"><figcaption><p>Every question shows its own prefill link. The parameter name is the question's <strong>Field key</strong>.</p></figcaption></figure>

The parameter name is the question's **Field key** (editable further down in the same section). The sample value changes with the question type: an email question shows `ana%40acme.com`, a phone question `%2B15555550123`, a slider a number, a choice question the value of its first option. A Name question lists both parameters (`firstname` and `lastname` by default).

> **💡 Tip:** Values in a URL must be URL-encoded: `@` becomes `%40`, `+` becomes `%2B`, spaces become `%20`. Most tools that build links do this for you.

***

**Step 2:** To pass data the respondent should not see, turn on **Hidden question** under **Behavior**. The hint reads **Not shown to respondents. Its answer is filled from a matching URL parameter (?key=value).** The card in the question list gets a **Hidden** badge.

<figure><img src="https://3835013762-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FCy5rSNtQmtqYCGzJlNEB%2Fuploads%2Fgit-blob-96e148b4b98ea99ea6362c46b2d07f53703a8303%2Fforms-hidden-fields-and-url-prefill-02-hidden-toggle.png?alt=media" alt="The editor with a Promo code question selected, the Hidden question switch turned on and the Hidden badge on the question card in the list"><figcaption><p>A hidden <strong>Promo code</strong> question with the key <code>promo</code>. Respondents never see it; the link fills it.</p></figcaption></figure>

A few details about hidden questions:

* **Hidden** is available for every type except Message, Reveal screen and Scheduler (those have nothing to store).
* A hidden question is skipped in the progress bar and the step count, and it never blocks the respondent, even if it is marked **Required**.
* Its value is still submitted, so you can map it to a HubSpot property, send it in a webhook, export it to CSV and recall it later with `[promo]`. Hidden questions never add to the score.
* If the link carries no value, the question's **Default answer** is used. If that is empty too, the answer is simply empty.

***

**Step 3:** Keep field keys away from `utm_`. Keys that start with `utm_` are never read from the URL: the editor shows **A key starting with utm\_ is never read from the URL: those are captured separately as campaign data. Rename the key to make prefill work.**

<figure><img src="https://3835013762-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FCy5rSNtQmtqYCGzJlNEB%2Fuploads%2Fgit-blob-0e79f5c71973cf042cb7164d356409ad8f26ec0d%2Fforms-hidden-fields-and-url-prefill-03-utm-warning.png?alt=media" alt="Advanced settings with the field key utm_promo and the red warning that a key starting with utm_ is never read from the URL"><figcaption><p>Rename the key (for example to <code>promo</code>) and prefill works again.</p></figcaption></figure>

You do not need a hidden question to track campaigns. `utm_source`, `utm_medium`, `utm_campaign`, `utm_term` and `utm_content` in the link are captured automatically with every submission and can be sent to HubSpot as form elements. Use hidden questions for anything that is not a UTM parameter: promo codes, lead source IDs, plan names, account IDs.

***

**Step 4:** Build the link and test it. Copy the example from the **Prefill from URL** block, replace `value`, and add more parameters with `&`:

```
https://forms.dapta.ai/k7m2xq/alex/lead-qualification-quiz?firstname=Ada&lastname=Lovelace&promo=SPRING25
```

<figure><img src="https://3835013762-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FCy5rSNtQmtqYCGzJlNEB%2Fuploads%2Fgit-blob-e99e7524ed6712a70b5a807ad0804cd972db2951%2Fforms-hidden-fields-and-url-prefill-04-public-prefilled.png?alt=media" alt="The published form opened from a link with firstname and lastname parameters: the name step shows Ada and Lovelace already filled in"><figcaption><p>Opened from the link above: the name step is already filled. The hidden <code>promo</code> value is stored silently.</p></figcaption></figure>

The respondent can still change a visible prefilled answer before moving on.

## How values are resolved

When a question has several possible sources, this is the order, from weakest to strongest:

| Priority    | Source                                 | Notes                                                                               |
| ----------- | -------------------------------------- | ----------------------------------------------------------------------------------- |
| 1 (lowest)  | **Default answer** (Advanced settings) | "Used when the link carries no value. Anything in the URL wins over this."          |
| 2           | **URL parameter** `?key=value`         | Applies to visible and hidden questions. Values longer than 512 characters are cut. |
| 3 (highest) | **What the respondent types**          | Only for visible questions.                                                         |

Other rules worth knowing:

* Prefill works for every question that stores a value: contact fields, choices (use the option **Value**, not the label), dropdowns, text, website, slider (a number inside min and max). Message, Reveal and Scheduler steps ignore it.
* A prefilled visible question still has to pass validation when the respondent continues (a bad email is not accepted just because it came from the link).
* Prefill also works inside an embedded form: add the parameters to the `src` of the iframe.
* Only parameters that match a field key of the form are read. Anything else in the URL is ignored.

## What's next

* [Question settings](/dapta-forms/builder/question-settings.md): field keys, default answers and what renaming a key changes.
* [Recall answers with @](/dapta-forms/builder/recall-answers.md): show a prefilled value in a later question.
* [Form elements: UTMs, score, outcome, submitted date](/dapta-forms/connect/hubspot/form-elements.md): send campaign data to HubSpot.
* [Your public link](/dapta-forms/share/public-link.md): where the public URL comes from.


---

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