How the Topics API works

The Topics API provides a privacy-preserving way to connect businesses with relevant audiences.

Topics assignment When someone browses the internet, the sites they visit are used to infer their generalized interest topics, such as sports.

Data management and protection These Topics are refreshed regularly and made available to API callers, without ever surfacing specific browsing information.

Bidding on private signals Marketers can then bid on the chance to serve ads to audiences with a particular topic, without identifying a specific person.

Here's a more detailed explanation of how it works:

1. Website mapping: Participating websites are mapped to a limited set of topics selected from a human-curated and publicly visible list. For example, a website about running might be associated with a "fitness" topic.
2. On-device topic calculation: Each week, your browser analyzes the sites you visit and calculates your top five topics based on those sites. This calculation happens locally on your device, so your browsing history is not shared with any external parties.
3. Limited topic sharing: When a website or ad tech platform wants to show you an ad, they can call the Topics API to request a few of your top topics. However, they can only receive topics that they have already "observed" for you recently, meaning topics associated with websites where they have previously interacted with the Topics API in your browser. This helps to prevent cross-site tracking and protect your privacy.