SourceTag

Form Setup

Set up SourceTag with Fillout

Fillout supports hidden fields that get populated when the form is embedded on your site. You define them in the form settings, and SourceTag fills them in with attribution data.

What you need

  • SourceTag installed on your website
  • A Fillout form embedded on your site using the JS embed

Step 1: Open your form in Fillout

Log in to Fillout and open the form you want to track.

[IMAGE: Screenshot of Fillout form editor]

Step 2: Add hidden fields

  1. In the form editor, go to Settings (or the form settings panel)
  2. Find the Hidden fields or URL parameters section
  3. Add a new hidden field for each SourceTag data point
  4. Set the field name to match the SourceTag field name exactly

[IMAGE: Screenshot of Fillout form settings showing the hidden fields section]

Core fields (add these)

  • st_fc_channel
  • st_fc_detail_1
  • st_fc_detail_2
  • st_fc_detail_3
  • st_fc_detail_4
  • st_lc_channel
  • st_lc_detail_1
  • st_lc_detail_2
  • st_lc_detail_3
  • st_lc_detail_4
  • st_fc_landing_page
  • st_lc_landing_page

Optional extended fields

If you have enabled extended field groups in your SourceTag dashboard, also add:

  • st_fc_click_id and st_lc_click_id (click IDs)
  • st_visits (visit count)
  • st_days_to_convert (days since first visit)
  • st_device (device type)

[IMAGE: Screenshot of Fillout hidden fields with all core fields configured]

Step 3: Embed on your site using JS embed

Fillout offers several embed methods. Use the JavaScript embed for best results with SourceTag.

Copy the embed code from Fillout’s sharing/embed settings and paste it onto your page. The page must also have the SourceTag script installed.

<!-- Your site already has SourceTag -->
<script src="https://cdn.sourcetag.io/scripts/YOUR_ID/st.js" async></script>

<!-- Fillout JS embed -->
<div data-fillout-id="YOUR_FORM_ID" data-fillout-embed-type="standard"></div>
<script src="https://server.fillout.com/embed/v1/"></script>

Avoid using the iframe embed if possible, as cross-origin restrictions can prevent SourceTag from reaching the form fields.

[IMAGE: Screenshot of Fillout embed options with JS embed selected]

Step 4: Test

Visit the page with UTM parameters:

?utm_source=test&utm_medium=cpc&utm_campaign=fillout-test

Submit the form. In Fillout, open the form’s Submissions and check the test entry. The hidden fields should show your attribution data.

[IMAGE: Screenshot of Fillout submission showing populated hidden fields]

Tips

  • Field names are case-sensitive. Copy them from the Fields page in your SourceTag dashboard.
  • The JS embed is the recommended method. If you must use an iframe, SourceTag will not be able to populate the fields.
  • Fillout integrations (Google Sheets, Zapier, Notion, etc.) will include hidden field values in the submission data.
  • If hidden fields come through empty, check your browser dev tools to confirm SourceTag is loaded on the page and the form is rendering within the same document (not in an iframe).