Cross-Domain Tracking

Overview

By default, the tracking script identifies visitors via first-party cookies, which are scoped to a single domain. If your visitor journey spans multiple domains (e.g., shop.example.com → checkout.payment.com), the visitor appears as a new visitor on each domain.

Cross-domain tracking solves this by passing the visitor's identity from one domain to another via URL parameters.

How It Works

When cross-domain tracking is enabled in the project settings:

The tracking script decorates outbound links with visitor cookie data as query parameters
When the visitor arrives on the destination domain, the tracking script reads these parameters
The visitor identity, session, and bucketing data are restored from the URL instead of cookies

URL Parameters Used

Parameter	Contains
`_conv_v`	Visitor cookie data (visitor ID, bucketing, goals, segments)
`_conv_s`	Session cookie data
`_conv_sptest`	Split test data (if applicable)

When these parameters are present in the URL, they override any existing cookies on the destination domain.

Enabling Cross-Domain Tracking

Enable the "Allow cross-domain tracking" setting in your Convert project configuration. The tracking script will then automatically:

Detect links to other domains in your page
Append the visitor parameters to those links
Read and restore visitor data from URL parameters on page load

Cookie Domain Configuration

For subdomains of the same root domain (e.g., www.example.com and shop.example.com), you may not need cross-domain tracking at all. Instead, configure the cookie domain in your project settings to the root domain (e.g., .example.com). This allows cookies to be shared across all subdomains automatically.

Security Considerations

URL parameters containing visitor data are not encrypted but contain no personally identifiable information — only a random visitor ID and experimentation state
Parameters are automatically URL-encoded
The visitor ID is a random hash, not tied to any personal data
Consider using HTTPS to prevent parameter interception in transit

Limitations

Cross-domain linking only works when the visitor navigates via a decorated link. Direct URL entry or bookmarks won't carry the parameters.
If the destination domain doesn't have the Convert tracking script installed, the parameters are ignored.
JavaScript-initiated navigation (e.g., window.location.href = url) may not be automatically decorated — you may need to append parameters manually in such cases.