How Topics are assigned to a site

The Topics API uses a sophisticated system to assign topics to websites. This process is designed to be transparent, accurate, and privacy-preserving.

Hostname-level assignment:

• Topics are assigned at the hostname level. This means that different subdomains of the same website can be assigned different topics. For example, sports.example.com and music.example.com would each be assigned their own topics.
• The content of individual pages is not considered when determining topics. This helps to protect user privacy and prevent the API from being used to infer sensitive information about specific pages.
• Currently, sites cannot directly specify the topics most relevant to their content.

Number of topics:

• There's no strict limit on the number of topics that can be associated with a site.
• On average, a site is assigned one or two topics.

Transparency and feedback:

• Anyone can view the topics inferred by the Topics classifier model for one or more hostnames.
• To view inferred topics, visit chrome://topics-internals and enter the hostname (without protocol or path) in the Classifier.
• If a site owner disagrees with the topics assigned to their site, they can provide feedback to Chrome via a new GitHub issue or relevant W3C groups (for example, the Improving Web Advertising Business Group or Private Advertising Technology Community Group).

Opting in or out of Topics:

• Only sites that use the Topics API or have embedded services (like ad tech tags) that use the Topics API will be included in Topics calculations.
• Sites can opt out of Topics using a Permissions Policy. This allows them to prevent embedded services from using the Topics API on their site.
• Sites that have already set the permissions policy for Google’s Federated Learning of Cohorts (FLoC) initiative will automatically be opted out of Topics.