The process of cookie syncing enables disparate ad tech platforms to align user identification through the exchange of unique identifiers. This coordination is necessary because cookies are limited by domain, restricting access to first-party data. As highlighted by Roesner et al. (2012), “cookie syncing allows third-party trackers to circumvent browser-enforced cookie isolation, leading to cross-site identification”. Participants in this process include advertisers, publishers, demand-side platforms (DSPs), supply-side platforms (SSPs), ad exchanges, and data management platforms (DMPs).
Key observations:
- User profiles are constructed by linking identifiers set by different platforms, enabling cross-site tracking and personalized advertising.
- Data sharing occurs via HTTP redirects, pixel tags, or JavaScript code snippets, which synchronously or asynchronously pass identifiers between systems.
- The process facilitates bid requests in real-time bidding (RTB) environments where multiple parties need a common understanding of each user: “Without cookie syncing, each partner sees an unconnected identifier, reducing the value of user data for targeting and attribution”.
- Privacy implications are significant; studies demonstrate that cookie syncing expands the reach of tracking far beyond what users expect or can control. “Cookie syncing increases the number of third parties that can track users, leading to greater privacy risks”.
- Regulatory frameworks such as the GDPR have placed constraints on these practices, with some platforms pursuing alternatives like server-side identity resolution and first-party data reliance.
In summary, cookie syncing is a technical workaround that connects user data across domains to support targeted digital advertising. While effective in constructing unified user profiles for marketing purposes, it exposes individuals to broader tracking and privacy risks, raising ongoing legal and ethical debates within the industry.
