Related Website Sets (RWS) is a collection or domains structured using three types of "subsets," each with specific use cases:
- Primary Domain: This is the main domain that other domains in the set are related to.
- Country Code Subset: This subset includes variations of the primary domain for different countries (for example, exampleA.co.uk, exampleA.jp). There is no limit on the number of domains in this subset.
- Service Subset: This subset includes domains that provide services to the primary domain (for example, service-exampleA.com). There is no limit on the number of domains in this subset.
- Associated Subset: This subset includes domains that are closely affiliated with the primary domain but may serve different content. For example, financial-news.example, tech-news.example. This subset is limited to five domains.
Why the limit on associated?
The limit on the Associated Subset is in place to prevent potential abuse and widespread tracking. Chrome initially proposed a limit of three domains, but based on feedback, it was increased to five to better align with industry practices and comparable implementations in other browsers.
Important considerations
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You can submit as many sets of five associated domains as needed.
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Sets are mutually exclusive; a domain can only belong to one Related Website Set.
How Chrome manages Related Website Sets information
Chrome regularly updates its canonical Related Website Sets list (every two weeks) and distributes it to clients as an updateable component. Individual clients refresh this list upon restarting or during startup if newly downloaded.
Alternatives to Related Website Sets
If you need to maintain functionalities like user sessions across more than five domains, consider using the Federated Credential Management (FedCM) API or the Storage Access API alone. These solutions offer alternative ways to enable seamless user experiences across multiple properties.