Custom Parameters

SourceTag captures UTM parameters and click IDs by default. But you might have other URL parameters you want to track. Custom parameters let you capture any arbitrary URL parameter and pass it into your forms.

How it works

1. You tell SourceTag which URL parameters to watch for
2. When a visitor lands on a page with that parameter in the URL, the value is captured and stored in the cookie alongside the rest of the attribution data
3. When the visitor submits a form, the value is populated into hidden fields named st_fc_custom_[name] (first click) and st_lc_custom_[name] (last click)

For example, if you configure brand as a custom parameter and a visitor arrives via:

https://yoursite.com/?utm_source=google&utm_medium=cpc&brand=acme

SourceTag will populate hidden fields st_fc_custom_brand and st_lc_custom_brand with the value acme when that visitor submits a form. Custom parameters follow the same first click / last click model as the rest of your attribution data.

Setting up custom parameters

1. In the SourceTag dashboard, go to your site’s Fields page
2. Scroll down to the Custom Parameters section
3. Add the URL parameter names you want to capture
4. Save your changes

Common use cases

Brand or product tracking

If you run campaigns for multiple brands or products under one domain, add brand or product as a custom parameter. Tag your ad URLs accordingly:

?utm_source=google&utm_medium=cpc&utm_campaign=summer-sale&brand=acme

This lets you attribute leads to specific brands within your CRM.

Affiliate or partner IDs

Track which affiliate or partner referred a lead:

?utm_source=partner-network&utm_medium=affiliate&affiliate_id=12345

Configure affiliate_id as a custom parameter. The hidden fields st_fc_custom_affiliate_id and st_lc_custom_affiliate_id will contain 12345.

Ad creative tracking

Go beyond utm_content with specific creative identifiers:

?utm_source=facebook&utm_medium=cpc&creative=video-testimonial-v2

Configure creative as a custom parameter to capture the creative variant.

Campaign-specific parameters

Any parameter your marketing team uses in URLs can be captured. Some examples:

Parameter	Example value	First click field	Last click field
brand	acme	st_fc_custom_brand	st_lc_custom_brand
affiliate_id	12345	st_fc_custom_affiliate_id	st_lc_custom_affiliate_id
creative	video-testimonial-v2	st_fc_custom_creative	st_lc_custom_creative
audience	retargeting-30d	st_fc_custom_audience	st_lc_custom_audience
region	us	st_fc_custom_region	st_lc_custom_region
offer	free-trial	st_fc_custom_offer	st_lc_custom_offer

How custom parameters are stored

Custom parameters are stored in the cookie as part of the first click and last click touch objects, just like UTMs and click IDs. They persist across page views and sessions.

• First click: The custom parameter values from the visitor’s first visit are stored permanently and never overwritten.
• Last click: Updated on each new visit that has attribution data (UTMs, click IDs, custom parameters, or an external referrer).

CRM field setup

When creating custom fields in your CRM to receive custom parameter data, you need fields for both first click and last click values. The internal field names must match the st_fc_custom_[name] and st_lc_custom_[name] format.

For example, if you’ve configured brand as a custom parameter:

• In HubSpot, create contact properties with internal names st_fc_custom_brand and st_lc_custom_brand
• In Salesforce, create custom lead fields with API names st_fc_custom_brand and st_lc_custom_brand
• In other CRMs, follow the same pattern

Tips

• Parameter names are case-sensitive. Brand and brand are treated as different parameters.
• Only parameters present in the URL are captured. If a visitor arrives without the parameter, no hidden field is created for that visit.
• You can add as many custom parameters as you need. There’s no hard limit.
• Make sure your marketing team knows which parameter names to use in their campaign URLs to keep things consistent.