Full Answer

Link decoration is Safari's term for URL parameters that tracking systems append to outbound links for attribution purposes. Google adds gclid to ad click URLs. Facebook adds fbclid. Microsoft Ads adds msclkid. These parameters allow the destination site's tracking scripts to connect the visit back to the specific ad that drove it.

Safari's ITP identifies these parameters through a machine-learning classifier that evaluates the referring domain's cross-site tracking behavior. When the classifier determines that the referring domain engages in cross-site tracking — which includes most advertising platforms — Safari applies the stricter 24-hour cookie cap to all JavaScript-set cookies on the destination page.

The practical impact on WooCommerce attribution is severe. A customer clicks a Google Shopping ad on their iPhone at 9am. The gclid parameter triggers Safari's link decoration detection. The GA4 _ga cookie and any attribution cookies set by JavaScript on your store expire at 9am the next day. If the customer returns to purchase at 10am on day two — just 25 hours later — the attribution cookie is already gone. GA4 records the purchase as a direct visit. Google Ads never receives the conversion signal.

This 24-hour window explains why Google Ads consistently reports fewer conversions than WooCommerce shows for the same period. The conversions happened — they just happened outside the window where Safari allowed the attribution cookie to exist.

Server-side tracking addresses this by capturing the gclid at the moment of click, storing it in the server-side session or database, and sending it back to Google Ads via Enhanced Conversions when the purchase occurs — days or weeks later. The gclid never needs to survive in a browser cookie because the server remembers it independently.