EngageTrack

Cross-Domain Tracking

Track visitors across multiple domains with seamless session stitching.

Cross-Domain Tracking

By default, EngageTrack treats each domain as a separate context. Cross-domain tracking lets you follow a single visitor across multiple domains (e.g., www.example.com to checkout.example.com) as one continuous session.

Cross-domain tracking requires storage mode (data-persistence="storage") on both domains. In the default memory mode, there is no persistent visitor ID to pass between domains. Storage mode requires a consent banner in the EU.

How It Works

  1. You list the destination domains in the data-allowed-hostnames attribute on the source domain
  2. When a visitor clicks a link to an allowed hostname, the SDK appends _et_vid (visitor ID) and _et_sid (session ID) as URL parameters
  3. On the destination domain, the SDK reads those parameters, hydrates the visitor and session IDs into localStorage/sessionStorage, and removes the parameters from the URL

The result is a seamless session that spans both domains.

Setup

Step 1: Configure the Source Domain

On every domain that links to another domain you own, add the destination hostnames to data-allowed-hostnames:

<!-- On www.example.com -->
<script
	defer
	data-site-id="YOUR_SITE_ID"
	data-persistence="storage"
	data-allowed-hostnames="checkout.example.com,app.example.com"
	src="https://cdn.engagetrack.net/sdk.js"
></script>

List only the exact hostnames (no protocol, no paths). Separate multiple hostnames with commas. Both data-persistence="storage" and data-allowed-hostnames are required on the source domain.

Step 2: Install the SDK on the Destination Domain

The destination domain must also have the EngageTrack script installed with the same site ID:

<!-- On checkout.example.com -->
<script
	defer
	data-site-id="YOUR_SITE_ID"
	data-persistence="storage"
	src="https://cdn.engagetrack.net/sdk.js"
></script>

The SDK automatically detects _et_vid and _et_sid in the URL, hydrates the visitor identity into localStorage/sessionStorage, and cleans the URL.

No special link markup is needed. The SDK intercepts clicks on outbound links and decorates them automatically:

<!-- This link will be decorated with _et_vid and _et_sid -->
<a href="https://checkout.example.com/buy">Complete Purchase</a>

Cross-domain links opened via window.open() or programmatic navigation are not automatically decorated. For those cases, build the URL manually using window.engagetrack.getVisitorId() and window.engagetrack.getSessionId().

Programmatic Navigation

If you navigate to a cross-domain URL with JavaScript:

const vid = window.engagetrack.getVisitorId();
const sid = window.engagetrack.getSessionId();
const url = new URL("https://checkout.example.com/buy");
url.searchParams.set("_et_vid", vid);
url.searchParams.set("_et_sid", sid);
window.location.href = url.toString();

Bidirectional Tracking

If visitors can navigate in both directions (e.g., www to checkout and back), add data-allowed-hostnames on both domains:

<!-- On www.example.com -->
<script
	defer
	data-site-id="YOUR_SITE_ID"
	data-persistence="storage"
	data-allowed-hostnames="checkout.example.com"
	src="https://cdn.engagetrack.net/sdk.js"
></script>
 
<!-- On checkout.example.com -->
<script
	defer
	data-site-id="YOUR_SITE_ID"
	data-persistence="storage"
	data-allowed-hostnames="www.example.com"
	src="https://cdn.engagetrack.net/sdk.js"
></script>

Verify It's Working

  1. Enable debug mode on both domains by adding data-debug="true" to the script tag
  2. Open the browser console on the source domain
  3. Click a link to the destination domain
  4. Look for [EngageTrack] Cross-domain link decorated: in the console — this confirms the URL parameters were appended
  5. On the destination domain, check for [EngageTrack] Cross-domain: hydrated visitor and hydrated session messages
  6. Verify both domains report the same visitor ID by calling window.engagetrack.getVisitorId() in the console on each domain