URL Prefill

Add query parameters to a URL and the form opens with those answers already filled in. Use it for campaign links, emails, and ads where you already know who the visitor is.

https://YOUR_WEBSITE.com/demo?<questionId>_<fieldName>=<value>

Where It Works

Where the form lives	Put the parameters on
Embedded with the Surface Tag (inline, popup, slideover, widget)	The URL of your page
Surface form link (`forms.withsurface.com/s/<formId>`)	The form link
Your own `<iframe>` without the Surface Tag	The iframe `src`

On a custom form domain, the Surface Tag needs data-custom-domain set, or the parameters never reach the form.

1. Find the Question ID

Open the form in the builder, select the question, and open the Behavior tab. Copy the Question ID.

2. Pick the Field Name

The part after the underscore depends on the question type.

Question type	Parameter	Value
Contact details	`<questionId>_<field>` (see below)	Any text
Short text	`<questionId>_input`	Any text
Long text	`<questionId>_input`	Any text
Dropdown	`<questionId>_selected`	Option text, exactly as shown
Multi-select dropdown	`<questionId>_selected`	Option texts, comma separated
Multiple options	`<questionId>_choices`	Option texts, comma separated

Contact Details Fields

Field	Field name
First name	`firstName`
Last name	`lastName`
Full name	`fullName`
Email	`emailAddress`
Work email	`workEmailAddress`
Phone	`phoneNumber`
Company	`companyName`
Job title	`title`
Website	`websiteUrl`
Company size	`numberOfEmployees`
Company revenue	`companyRevenue`
Street address	`streetAddress`
Apt, suite	`aptSuiteEtc`
City	`city`
State	`state`
Zip code	`zipCode`
Country	`country`

3. Build the URL

Join parameters with &. One contact details question can take several fields.

https://YOUR_WEBSITE.com/demo?abc123_firstName=Jane&abc123_emailAddress=jane%40acme.com&def456_selected=United%20States

Replace abc123 and def456 with your question IDs.

Rules

Option values must match the option text exactly, including case. Values that match nothing are ignored.
A comma always separates options, so an option containing a comma cannot be prefilled.
URL-encode values: space is %20, @ is %40, + is %2B.
An email field that blocks personal emails ignores a personal address from the URL.
url, referrer, and cookies are reserved parameter names.
Other parameters (utm_*, gclid) are untouched and still attribute the visit.
Visitors can edit prefilled answers before submitting.

Not Supported

Single choice questions (pick one buttons).
Multiple options questions on a Surface form link. They prefill only when embedded with the Surface Tag.