URL Parameters/Hidden fields

URL parameters are a powerful way to pass information to a Fillout form to support pre-filling and personalizing the form.


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 users. For example:
  • Pre-filling fields with the email of the user if you already know it
  • Recording where your form was shared via a utm_source parameter (e.g. Facebook, Google, Instagram, etc.)
  • Displaying the user’s name in the form to welcome them

How to add a URL parameter or Hidden field

1. Register a new parameter

The first step is to "register" a URL parameter. Go to the settings tab and click URL parameters.
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Then press Add new to add a new URL parameter. Here, we can tell Fillout to expect a URL Parameter with a certain name.
Adding an “email” URL parameter or hidden field
Adding an “email” URL parameter or hidden field
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 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 tab at the top and creating a new connection or editing an existing one, and mapping this URL Parameter to some field in e.g. Airtable/Notion.
  • Display in plaintext in the form

3. Share your form link with the URL parameter set

To have the URL parameter be active in your form, you need to set its value in the form link you share with users.
For example, if we have a parameter called email registered, and we know that the user’s email that we’re sending our form to is “jane@gmail.com”, we can send a link that looks like this: https://forms.fillout.com/t/your_form_id?email=jane@gmail.com
When you have multiple URL parameters for one form, you’ll need to separate them using an ampersand (&), like so: https://forms.fillout.com/t/your_form_id?email=jane@gmail.com&name=jane

Example uses

Personalize a form with URL parameters

  1. Type "@" in any question or heading to reference information from your form
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  1. Click "continue" into the "URL parameters" section
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3. "Insert" the URL parameter which you have registered, and then try out your form with an example URL parameter in preview or live mode!
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Recording URL parameters in submissions

Often, you will want to record which URL parameters were passed when submitting the form. A common scenario would be that you're pasting the link to your form on various social media platforms (e.g. Facebook, Instagram, Linkedin), and you want to see which ones get a higher percentage of traffic. By default, Fillout stores the URL parameters used in a submission on the results page (see below).
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If you're using an integration, and want to write your URL parameters there as well, you can either:
a) Create a Fillout field and pre-fill it with a URL parameter, and then "Always hide" it on the right-hand settings panel. If this field is synced to an integration already, then it will automatically write to your integration without ever being visible to the user:
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b) Head to your integration settings, and map the URL parameter directly. E.g. for Airtable, there is an "Mappings" section which you can use for this purpose. See this article for more information.