What is cross-site tracking?

Cross-site tracking connects activity across different websites to recognise the same person or browser and build a broader picture of their behaviour. It is commonly used for advertising, audience profiling and measuring user journeys across websites.

A typical example is an advertising provider embedded on multiple websites. If it can recognise the same browser on each site, it can connect those visits rather than treating them as separate interactions.

Cross-site tracking can involve:

• Third-party cookies that provide a shared identifier across websites.

• Identifiers passed through links that connect activity between websites.

• Browser fingerprinting that can help recognise the same browser without a conventional cookie.

First-party tracking is generally performed by the website a user is visiting, while third-party tracking involves an external provider that may operate across multiple websites. Cross-site tracking is therefore often associated with third-party services, although the technologies involved can vary.

Blocking third-party cookies can restrict one method of cross-site tracking, but it does not necessarily prevent other techniques such as link-based identifiers or browser fingerprinting. WebKit’s tracking prevention policy describes several techniques relevant to cross-site tracking.

For website operators, it is important to check whether a provider combines visitor activity with information collected from other websites or contexts. A tool described as “analytics” may still support cross-site tracking depending on how it is implemented.