Cookie syncing

Cookie syncing (or cookie matching) is a process that synchronizes cookies and shares user information across different platforms so that every platform involved in an ad transaction has a common understanding of the audience.

Cookies are domain-specific, meaning cookies created by one domain (e.g., can’t be read by another domain (e.g.,

When an AdTech platform’s tag is added to a website, it can create a cookie under its domain and save it to the user’s device by sending a request from the website to its server. However, this cookie is specific to the AdTech company’s domain and would differ from those created by the website and other AdTech companies.

This makes it difficult for AdTech companies to identify the same user across different domains (aka websites). User identification is needed for behavioral ad targeting and many other essential advertising processes.

The solution lies in cookie syncing. It’s a process whereby unique user identifiers stored in Cookies are matched between advertising systems, e.g., AdTech platforms, to identify the users and exchange information about them.

The main goal of cookie syncing is to recognize users across different sites, also known as cross-site tracking. Identifying a user across the web allows advertisers to improve ad targeting, display ads to audiences they’ve created in a Data management platform (DMP), run frequency capping, and measure and attribute impressions, clicks, and conversions.

This cookie-syncing process is carried out by most advertising technology platforms, such as:

  • Ad networks
  • Demand-side platforms (DSPs)
  • Data-management platforms (DMPs)
  • Ad exchanges
  • Supply-side platforms (SSPs)