Overview

URL parameters, also known as “hidden fields”, can be used to customize your form with information you already know when you’re sharing it with respondents. For example:

• Pre-filling fields with the email of the respondent
• Recording where your form was shared via a utm_source parameter (e.g. Facebook, Google, Instagram, etc.)
• Displaying the respondent's name in the form to welcome them

How to add a URL parameter or hidden field

1. Register a new parameter

Go to Settings and click URL parameters. Then, click + Add new

Enter a Parameter name. Here, we can tell Fillout to expect a URL Parameter with a certain name.

Note that you can optionally provide a sample value for the parameter, if you’d like to see what your form looks like with that value being used (e.g. if you have some hide/show logic based on it).

2. Use the parameter in your form

You’re all set to start using your new URL parameter now! We can now use it to:

• Pre-fill a field, by pressing the + icon on a Default value property of any field
• Write to any integration, by heading to the Integrations at the top and creating a new connection or editing an existing one, and mapping this URL Parameter to some field like in Airtable or Notion.
• Display in plaintext in the form

3. Share your form link

To make the URL parameter active in your form, you need to set its value in the form link you share with respondents. For example, if we have a parameter called name registered, the default link would look like: https://forms.fillout.com/t/9ofaEF4d54us?name=xxxxx