Cross-Domain Tracking - DATALYR Documentation

Cross-domain tracking enables DATALYR to follow users as they navigate between different domains and subdomains, maintaining attribution and user identity throughout their journey.

What is Cross-Domain Tracking

Cross-domain tracking links user sessions and attribution data across:

Multiple domains (example.com → shop.example.com)
Subdomains (www.example.com → app.example.com → blog.example.com)
Third-party checkout (yoursite.com → checkout.stripe.com → yoursite.com)
Payment processors (yoursite.com → paypal.com → yoursite.com)

How It Works

Cross-Subdomain Tracking (Automatic)

DATALYR automatically tracks visitors across subdomains using root domain cookies. Example: www.example.com → app.example.com Step 1: First Visit (www.example.com)

// User visits www.example.com
// DATALYR generates: anon_abc123
// Sets cookie: __dl_visitor_id=anon_abc123; domain=.example.com

Step 2: Navigate to Subdomain (app.example.com)

// User clicks link to app.example.com
// DATALYR reads cookie from .example.com
// Uses same ID: anon_abc123
// Journey continues seamlessly

Result: Same visitor ID across all subdomains, complete journey tracking. DATALYR sets visitor ID cookie on the root domain (e.g., .example.com): Cookie Attributes:

__dl_visitor_id=anon_f47ac10b-58cc-4372-a567-0e02b2c3d479;
domain=.example.com;
path=/;
max-age=31536000;
SameSite=Lax;
Secure

Accessible On:

example.com
www.example.com
app.example.com
blog.example.com
shop.example.com
Any subdomain of example.com

Not Accessible On:

different-domain.com (different root domain)
example.org (different TLD)

Supported Domain Types

Standard TLDs

Format: domain.tld Examples:

example.com → Cookie: .example.com
myshop.net → Cookie: .myshop.net
startup.io → Cookie: .startup.io

Subdomains Tracked:

www.example.com
app.example.com
api.example.com

Country-Specific TLDs

Format: domain.co.tld or domain.com.tld Supported Two-Part TLDs:

.co.uk (United Kingdom)
.com.au (Australia)
.co.nz (New Zealand)
.co.jp (Japan)
.co.in (India)
.co.za (South Africa)

Examples:

example.co.uk → Cookie: .example.co.uk
myshop.com.au → Cookie: .myshop.com.au

Subdomains Tracked:

www.example.co.uk
shop.example.co.uk
blog.example.co.uk

Localhost and IP Addresses

Localhost:

localhost → Cookie: localhost

IPv4:

192.168.1.1 → Cookie: 192.168.1.1

IPv6:

[::1] → Cookie: [::1]

Cross-Domain Tracking (Multiple Domains)

When users navigate between different domains (not just subdomains), you need to pass visitor ID in the URL.

URL Parameter Method

DATALYR automatically reads the _dl_vid parameter from URLs on page load. However, you need to manually append the parameter to links when navigating to different domains. How it works:

You append _dl_vid to outbound links (manual step)
DATALYR automatically reads _dl_vid on the destination page (automatic)
The visitor ID is preserved across domains

Manual Linking (Required):

// Get visitor ID
const visitorId = datalyr.getAnonymousId();

// Append to checkout URL
const checkoutUrl = `https://checkout.example.com?_dl_vid=${visitorId}`;

// Redirect
window.location.href = checkoutUrl;

On Destination Domain:

// DATALYR automatically reads _dl_vid from URL on page load
// The visitor ID from the URL is used and stored in cookies/localStorage
// Journey continues seamlessly with the same visitor ID

Use Cases

E-commerce with Third-Party Checkout:

yourstore.com → shopify.com/checkout → yourstore.com/thank-you

Payment Processors:

yoursite.com → stripe.com/checkout → yoursite.com/success
yoursite.com → paypal.com/checkout → yoursite.com/success

Multi-Site Funnels:

landing-page.com → signup.example.com → app.example.com

Affiliate Networks:

affiliate-site.com → your-offer.com

Implementation Examples

Cross-Subdomain Setup (Automatic)

No additional setup required. DATALYR automatically tracks across subdomains. Install on Each Subdomain: www.example.com:

<script defer src="https://track.datalyr.com/dl.js" data-workspace-id="ws_123"></script>

app.example.com:

<script defer src="https://track.datalyr.com/dl.js" data-workspace-id="ws_123"></script>

shop.example.com:

<script defer src="https://track.datalyr.com/dl.js" data-workspace-id="ws_123"></script>

Result: Visitor ID shared automatically via .example.com cookie.

Cross-Domain Setup (Manual)

Pass visitor ID between different domains: Source Domain (yoursite.com):

// Add visitor ID to checkout link
document.addEventListener('DOMContentLoaded', function() {
  const checkoutLinks = document.querySelectorAll('a[href*="checkout.example.com"]');

  checkoutLinks.forEach(link => {
    const visitorId = datalyr.getAnonymousId();
    const url = new URL(link.href);
    url.searchParams.set('_dl_vid', visitorId);
    link.href = url.toString();
  });
});

Destination Domain (checkout.example.com):

<!-- Install DATALYR - it automatically reads _dl_vid from URL on init -->
<script defer src="https://track.datalyr.com/dl.js" data-workspace-id="ws_123"></script>
<!-- The visitor ID from ?_dl_vid=anon_abc123 will be used automatically -->

Return Domain (yoursite.com/thank-you):

// Visitor ID persists via cookie on yoursite.com
// Journey is complete and tracked

Form Submission to Different Domain

Form on yoursite.com:

<form id="checkout-form" method="POST" action="https://checkout.example.com">
  <input type="hidden" name="product_id" value="SKU123">
  <!-- Visitor ID will be added by JavaScript -->
  <button type="submit">Checkout</button>
</form>

<script>
document.getElementById('checkout-form').addEventListener('submit', function(e) {
  e.preventDefault();

  const form = e.target;
  const visitorId = datalyr.getAnonymousId();

  // Add visitor ID as hidden field
  const input = document.createElement('input');
  input.type = 'hidden';
  input.name = '_dl_vid';
  input.value = visitorId;
  form.appendChild(input);

  // Submit form
  form.submit();
});
</script>

Checkout page reads visitor ID:

// checkout.example.com - DATALYR automatically reads _dl_vid from URL
// Note: POST data reading requires server-side implementation
// URL parameter method is recommended for client-side tracking

Attribution Across Domains

Cross-domain tracking preserves attribution data across domain boundaries.

Example: Multi-Domain Purchase Journey

Day 1: Landing Page (landing.example.com)

User clicks Facebook ad
URL: https://landing.example.com/?utm_source=facebook&utm_medium=cpc&fbclid=IwAR123
DATALYR captures:
  - anonymous_id: anon_abc123
  - utm_source: facebook
  - utm_medium: cpc
  - fbclid: IwAR123
  - Cookie set: .example.com

Day 2: Main Site (www.example.com)

User navigates to www.example.com
DATALYR reads cookie from .example.com
Same visitor ID: anon_abc123
Attribution preserved: facebook / cpc / IwAR123

Day 3: App (app.example.com)

User signs up on app.example.com
DATALYR identifies user:
  - anonymous_id: anon_abc123 → user_id: user_456
  - Attribution still preserved

Day 7: Checkout (checkout.stripe.com)

User clicks checkout button
Redirected to: checkout.stripe.com?_dl_vid=anon_abc123
Stripe processes payment
Returns to: www.example.com/thank-you?_dl_vid=anon_abc123

Day 7: Thank You Page (www.example.com)

DATALYR tracks purchase event:
  - anonymous_id: anon_abc123
  - user_id: user_456
  - Attribution: facebook / cpc / IwAR123

Purchase correctly attributed to Facebook ad from Day 1!

Identity Across Domains

When users identify (login/signup) on any domain, their identity links across all tracked domains. Example: Domain 1 (www.example.com):

// User browses anonymously
// anonymous_id: anon_abc123

Domain 2 (app.example.com):

// User signs up
datalyr.identify('user_456', {
  email: '[email protected]'
});

// Links: anon_abc123 → user_456

Domain 3 (shop.example.com):

// User purchases
datalyr.track('purchase', {
  order_id: 'ORDER_123',
  revenue: 99.99
});

// Automatically attributed to user_456
// Includes original attribution from Domain 1

Troubleshooting

Visitor ID Changes Across Subdomains

Symptoms:

Different visitor IDs on different subdomains
Journeys not linked

Common Causes: 1. Cookie Blockers Browser extensions or privacy tools blocking third-party cookies. Solution:

// Check if cookies are blocked
console.log('Cookie available:', document.cookie.includes('__dl_visitor_id'));

2. Incorrect Root Domain Cookie set on wrong domain scope. Check:

// Open browser DevTools → Application → Cookies
// Verify: __dl_visitor_id cookie domain is ".example.com" not "www.example.com"

3. HTTPS/HTTP Mismatch Secure cookie not accessible on HTTP subdomain. Solution: Ensure all subdomains use HTTPS. 4. SameSite Cookie Restrictions Browser blocking cross-site cookie access. Solution: DATALYR uses SameSite=Lax which allows same-site subdomain access.

Visitor ID Not Passed Between Domains

Symptoms:

New visitor ID generated on different domain
Attribution lost

Solutions: 1. Manual URL Parameter Add _dl_vid to links:

const visitorId = datalyr.getAnonymousId();
const url = `https://checkout.com?_dl_vid=${visitorId}`;

2. Form Hidden Field Include visitor ID in form submissions:

<input type="hidden" name="_dl_vid" value="[visitor_id]">

3. localStorage Fallback If cookies blocked, use localStorage + URL parameter:

// Source domain
const visitorId = datalyr.getAnonymousId();
localStorage.setItem('dl_cross_domain_vid', visitorId);

// Destination domain
const crossDomainVid = new URLSearchParams(window.location.search).get('_dl_vid');
if (crossDomainVid) {
  localStorage.setItem('dl_anonymous_id', crossDomainVid);
}

Attribution Lost After Domain Change

Symptoms:

Source/medium changes to “direct” after crossing domains
UTM parameters lost

Solutions: 1. Preserve UTM Parameters Include UTM parameters when linking between domains:

const currentParams = new URLSearchParams(window.location.search);
const utmParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content'];

const url = new URL('https://checkout.example.com');
utmParams.forEach(param => {
  if (currentParams.get(param)) {
    url.searchParams.set(param, currentParams.get(param));
  }
});

window.location.href = url.toString();

2. Preserve Click IDs Include fbclid, gclid, etc.:

const clickIds = ['fbclid', 'gclid', 'ttclid', 'li_fat_id'];
clickIds.forEach(id => {
  if (currentParams.get(id)) {
    url.searchParams.set(id, currentParams.get(id));
  }
});

Best Practices

Install Tracking on All Domains/Subdomains

<!-- Install on every domain and subdomain -->
<script defer src="https://track.datalyr.com/dl.js" data-workspace-id="ws_123"></script>

Use Same Workspace ID All domains/subdomains must use the same data-workspace-id. Call identify() After Login Identify users immediately after login on any domain:

// After successful login on any domain
datalyr.identify(user.id, {
  email: user.email
});

Preserve URL Parameters Don’t strip UTM parameters or click IDs when redirecting between domains. Use HTTPS Everywhere Secure cookies require HTTPS. Use HTTPS on all domains/subdomains. Test Cookie Persistence

// Check cookie on different subdomains
console.log('Visitor ID:', datalyr.getAnonymousId());
console.log('Cookie:', document.cookie.match(/__dl_visitor_id=([^;]+)/));

Advanced Configuration

Custom Domain for Checkout

Scenario: Checkout hosted on checkout.yoursite.com but different infrastructure. Solution:

// Main site (www.yoursite.com)
<script defer src="https://track.datalyr.com/dl.js" data-workspace-id="ws_123"></script>

// Checkout site (checkout.yoursite.com)
<script defer src="https://track.datalyr.com/dl.js" data-workspace-id="ws_123"></script>

// Cookie automatically shared via .yoursite.com

Multi-Brand Tracking

Scenario: Track users across multiple brand domains (brand1.com, brand2.com). Solution:

// Pass visitor ID via URL between brands
const visitorId = datalyr.getAnonymousId();

// Redirect to other brand
window.location.href = `https://brand2.com?_dl_vid=${visitorId}`;

// Track as same visitor across brands

Next Steps

Visitor Identification

How DATALYR identifies visitors

Identity Calls

Link users across sessions

Attribution Models

How attribution works

Customer Journeys

View complete user paths

Need Help?

Questions about cross-domain tracking? Check our troubleshooting guide or contact support.

Introduction

Getting Started

Installation

Container & Tag Management

Understanding Your Data

Integrations

Features

Account & Billing

SDKs & Developer Tools

Troubleshooting

​What is Cross-Domain Tracking

​How It Works

​Cross-Subdomain Tracking (Automatic)

​Root Domain Cookie

​Supported Domain Types

​Standard TLDs

​Country-Specific TLDs

​Localhost and IP Addresses

​Cross-Domain Tracking (Multiple Domains)

​URL Parameter Method

​Use Cases

​Implementation Examples

​Cross-Subdomain Setup (Automatic)

​Cross-Domain Setup (Manual)

​Form Submission to Different Domain

​Attribution Across Domains

​Example: Multi-Domain Purchase Journey

​Identity Across Domains

​Troubleshooting

​Visitor ID Changes Across Subdomains

​Visitor ID Not Passed Between Domains

​Attribution Lost After Domain Change

​Best Practices

​Advanced Configuration

​Custom Domain for Checkout

​Multi-Brand Tracking

​Next Steps

Visitor Identification

Identity Calls

Attribution Models

Customer Journeys

​Need Help?

What is Cross-Domain Tracking

How It Works

Cross-Subdomain Tracking (Automatic)

Root Domain Cookie

Supported Domain Types

Standard TLDs

Country-Specific TLDs

Localhost and IP Addresses

Cross-Domain Tracking (Multiple Domains)

URL Parameter Method

Use Cases

Implementation Examples

Cross-Subdomain Setup (Automatic)

Cross-Domain Setup (Manual)

Form Submission to Different Domain

Attribution Across Domains

Example: Multi-Domain Purchase Journey

Identity Across Domains

Troubleshooting

Visitor ID Changes Across Subdomains

Visitor ID Not Passed Between Domains

Attribution Lost After Domain Change

Best Practices

Advanced Configuration

Custom Domain for Checkout

Multi-Brand Tracking

Next Steps

Need Help?