The hidden field stores a string from a URL parameter or configured default without rendering a control.
Options
| Option | Type | Default | Behavior |
|---|---|---|---|
paramName | string | the field ID | Selects the query-string key |
defaultValue | string | none | Supplies a value when the parameter is absent |
Hidden-field parameter names are case-sensitive. A URL value wins over defaultValue, while explicit SDK initialData and a respondent's typed state win over URL prefill.
Add a hidden field
In the dashboard, select Add block, choose Hidden, and set the parameter name and optional default.
ts
const sourceField = {
id: "campaign_source",
kind: "hidden",
label: "Campaign source",
paramName: "utm_source",
defaultValue: "direct",
} as const;Opening /f/contact?utm_source=newsletter stores newsletter under the stable response key campaign_source.
Related
- Prefill and hidden fields: See the full precedence and coercion rules.
- Capture UTM and attribution data: Record campaign parameters with stable response keys.
- Prefill from your app session: Pass known account context directly from the host app.