Topics API
What is Topics API?
Topics APIA Privacy Sandbox API in Chrome and Android that derives a small set of high-level interest topics from the user's recent browsing locally on the device, exposing them to participating sites instead of cross-site tracking identifiers.
The Topics API is a Privacy Sandbox component that replaces third-party-cookie-based behavioural interest signals with a locally derived, low-resolution interest taxonomy. Chrome (and Android) infers, on device, up to a few coarse topics — drawn from a public taxonomy of a few hundred categories such as 'Sports/Soccer' or 'Travel/Hotels & Accommodations' — based on the top-level hostnames the user has visited over the past few weeks. When a caller invokes `document.browsingTopics()`, the browser returns a small random sample of recent topics (with random noise to limit linkability), but only for hostnames that were observed by that caller in the past. This means a fingerprinter sitting on a single site cannot ask for topics on behalf of unrelated callers, and a site cannot use the topics as a stable identifier. Critics — Mozilla, Brave, the EFF, several DPAs — have argued the API still reveals more than necessary and effectively endorses behavioural advertising at the browser level. Google launched Topics for general availability in Chrome in 2023 and on Android in 2024; uptake by ad-tech players grew through 2024–2025 in tandem with Privacy Sandbox.
● Examples
- 01
An ad-tech vendor calls `document.browsingTopics()` from its tag on a sports site, receives `Sports/Soccer` for that user, and uses it as a contextual signal.
- 02
A regulator's analysis observes that, even with topic noise, frequent callers can build short-lived behavioural cohorts and flags the API for further review.
● Frequently asked questions
What is Topics API?
A Privacy Sandbox API in Chrome and Android that derives a small set of high-level interest topics from the user's recent browsing locally on the device, exposing them to participating sites instead of cross-site tracking identifiers. It belongs to the Privacy & Data Protection category of cybersecurity.
What does Topics API mean?
A Privacy Sandbox API in Chrome and Android that derives a small set of high-level interest topics from the user's recent browsing locally on the device, exposing them to participating sites instead of cross-site tracking identifiers.
How does Topics API work?
The Topics API is a Privacy Sandbox component that replaces third-party-cookie-based behavioural interest signals with a locally derived, low-resolution interest taxonomy. Chrome (and Android) infers, on device, up to a few coarse topics — drawn from a public taxonomy of a few hundred categories such as 'Sports/Soccer' or 'Travel/Hotels & Accommodations' — based on the top-level hostnames the user has visited over the past few weeks. When a caller invokes `document.browsingTopics()`, the browser returns a small random sample of recent topics (with random noise to limit linkability), but only for hostnames that were observed by that caller in the past. This means a fingerprinter sitting on a single site cannot ask for topics on behalf of unrelated callers, and a site cannot use the topics as a stable identifier. Critics — Mozilla, Brave, the EFF, several DPAs — have argued the API still reveals more than necessary and effectively endorses behavioural advertising at the browser level. Google launched Topics for general availability in Chrome in 2023 and on Android in 2024; uptake by ad-tech players grew through 2024–2025 in tandem with Privacy Sandbox.
How do you defend against Topics API?
Defences for Topics API typically combine technical controls and operational practices, as detailed in the full definition above.
What are other names for Topics API?
Common alternative names include: Browsing Topics API.
● Related terms
- privacy№ 960
Privacy Sandbox
Google's umbrella initiative for replacing third-party cookies and cross-site identifiers with privacy-preserving alternatives — Topics, Protected Audience (FLEDGE), Attribution Reporting, and on-device APIs — under heavy regulatory and competitor scrutiny.
- privacy№ 088
Attribution Reporting API
A Privacy Sandbox API in Chrome and Android that lets advertisers measure ad conversions across sites without cross-site identifiers, using browser-mediated, noise-injected event-level or aggregated reports.
- privacy№ 1263
Third-Party Cookie
A cookie set by a domain different from the one in the browser's address bar, historically used to track users across websites.
- privacy№ 143
Browser Fingerprinting
A stateless tracking technique that identifies a user by combining browser, device, and configuration attributes into a near-unique signature.
- privacy№ 266
Cross-Site Tracking
The practice of linking a user's activity across multiple unrelated websites to build a long-lived behavioural profile.
- privacy№ 914
Personally Identifiable Information (PII)
Any data that can identify a specific individual on its own or when combined with other information, such as names, identifiers, or biometric records.