WTH are Related Website Sets? Unpacking Google’s Privacy Sandbox Initiative

April 3, 2024

Introduction to First-Party Sets and the Transition to Related Website Sets (RWS)

In the evolving landscape of digital privacy, web browsers are phasing out third-party cookies to enhance user privacy. This shift, however, presents challenges for organizations that operate across multiple domains and rely on cookies for seamless user experiences. Enter the concept of First-Party Sets, a framework that allowed related domains to declare their association, thereby enabling certain cross-site functionalities. As the digital ecosystem continues to adapt, Google has refined this approach with the introduction of Related Website Sets (RWS).

RWS is a pivotal development in the Privacy Sandbox initiative, aiming to balance user privacy with essential web functionalities. It enables companies to formally declare relationships among their various domains, allowing browsers like Chrome to grant limited third-party cookie access for specific, user-centric purposes. This transition from First-Party Sets to RWS marks a significant step towards a more privacy-conscious web, where user journeys across different domains of the same entity can continue without the privacy concerns associated with third-party cookies. As we approach the deprecation of third-party cookies in 2024, understanding RWS becomes crucial for web developers and organizations to maintain cohesive digital experiences while respecting user privacy.

Understanding the Privacy Sandbox: A Shift from Third-Party Cookies

In the digital ecosystem, third-party cookies have long been the linchpin of online tracking, advertising, and user experience personalization. However, with growing concerns over privacy, the industry is witnessing a paradigm shift. Enter Google's Privacy Sandbox, an initiative that promises to reshape the web by phasing out third-party cookies and introducing privacy-centric alternatives.

The Privacy Sandbox is a suite of APIs designed to protect users' privacy while still allowing advertisers and websites to deliver personalized experiences and measure performance. One of the key components of this initiative is the Related Website Sets (RWS), which allows organizations to group their related domains together. This grouping enables limited third-party cookie access for specific purposes, such as maintaining user sessions across different domains owned by the same entity.

The shift is significant: instead of relying on third-party cookies that track users across the entire web, RWS confines user identification to a controlled set of related websites. This approach upholds user privacy by limiting the scope of tracking while preserving essential functionalities like single sign-on and seamless navigation across affiliated domains.

As the Privacy Sandbox continues to evolve, it's crucial for stakeholders to understand the implications of these changes. The move away from third-party cookies to solutions like RWS represents a balancing act between user privacy and the operational needs of online services. It's a step towards a more private web, but one that requires adaptation and a new understanding of digital interactions.

The Mechanics of Related Website Sets: How They Work

Related Website Sets (RWS) operate on a straightforward yet nuanced principle: they allow organizations to declare a consortium of domains as related entities. This declaration is pivotal as it informs the browser to treat these domains as a cohesive unit, particularly when handling third-party cookies. The mechanics of RWS are rooted in the need to balance user privacy with seamless web functionality.

At the core of RWS is the concept of a "set primary" domain—the main domain representing the organization—and multiple "set members," which are the additional domains associated with the primary. To form a Related Website Set, site authors submit their domains for inclusion, establishing a clear relationship between the primary and its members. This relationship is critical for browsers, like Chrome, which use this information to determine when to permit or deny cookie access in third-party contexts.

Once a set is established, browsers can grant limited third-party cookie access for specific purposes. This means that as a user navigates through the related domains within the set, their experience remains uninterrupted. For instance, a shopping cart can retain items as a customer moves from a brand's main shopping site to its affiliated checkout domain.

The RWS framework is designed with abuse mitigation in mind, ensuring that domains cannot be arbitrarily added to multiple sets or without proper authorization. This is enforced through technical checks and a public submission process that promotes transparency and accountability.

In essence, RWS is a meticulous system that preserves user journeys across related domains while upholding the stringent privacy standards set forth by the evolving web ecosystem. It's a delicate dance between connectivity and confidentiality, choreographed to keep the user's experience at the forefront without compromising their privacy.

Key Use Cases for Related Website Sets: From Sign-Ons to Analytics

Related Website Sets (RWS) serve as a pivotal mechanism within Google's Privacy Sandbox initiative, designed to preserve essential web functionalities in the absence of third-party cookies. These use cases are not only fundamental to maintaining a seamless user experience but also crucial for website operators to manage their digital ecosystems effectively.

  1. Single Sign-On Across Multiple Domains: RWS facilitates a unified sign-on experience for users navigating through related web properties. For instance, a user logged into a primary domain can seamlessly access affiliated services or subdomains without the need to re-authenticate. This is particularly beneficial for conglomerates with multiple service offerings under different domains.
  2. Cross-Domain Analytics and Measurement: Analytics is the backbone of understanding user behavior and improving service offerings. RWS allows organizations to track user interactions across their related domains, providing a holistic view of user journeys. This aggregated data is instrumental in refining user experience and tailoring services to meet user needs more precisely.
  3. Content Personalization Across Brands: Brands with multiple online touchpoints can leverage RWS to personalize content across their domain sets. A user's preferences and interactions on one site can inform the content presented on another, creating a customized and consistent brand experience.
  4. Securely Isolating User-Uploaded Content: For security reasons, user-generated content is often hosted on separate domains to mitigate risks. RWS ensures that while the content is isolated for security, authentication and user preferences can still be shared across the primary and sandboxed domains.

By addressing these key use cases, RWS aims to strike a balance between enhancing user privacy and enabling the functionality that users have come to expect from the web. As we move towards a more privacy-conscious era, RWS stands as a testament to the evolving web landscape, where user experience and privacy go hand in hand.

The Impact on User Experience: Seamless Browsing Across Domains

In the evolving landscape of digital privacy, the user experience remains paramount. As Google phases out third-party cookies, the introduction of Related Website Sets (RWS) within the Privacy Sandbox initiative is a beacon of continuity for seamless browsing. This change heralds a significant shift in how users interact with multi-domain entities without compromising the convenience they have come to expect.

Imagine a user navigating through a suite of services offered by a single entity across different domains. Prior to RWS, third-party cookies facilitated a frictionless experience, remembering user preferences, login states, and shopping carts as they traversed related sites. With RWS, this user-centric functionality is preserved. Users can still move across domains—be it from a service page to a product page or between country-specific sites—without the jarring necessity of repeated sign-ins or loss of context. The experience is akin to walking through different rooms of the same house, as opposed to entering through the front door each time one switches rooms.

For the end-user, RWS ensures that the web remains as responsive and personalized as ever, while aligning with modern privacy standards. The user journey remains uninterrupted, fostering brand loyalty and user satisfaction. In essence, RWS offers a balanced solution that maintains the fluidity of the digital experience, while erecting robust privacy protections that are becoming the new norm in our interconnected world.

Technical Requirements: Setting Up and Submitting Related Website Sets

To successfully implement Related Website Sets (RWS), site authors must navigate a series of technical requirements that ensure proper setup and submission. The process begins with the identification of a "set primary"—the main domain representing the collection of related domains, or "set members."

Firstly, site authors need to verify ownership of all domains included in the set. This involves placing a .well-known resource on each domain, which contains the RWS manifest linking back to the set primary. The manifest must be accessible via HTTPS to ensure secure communication.

Once ownership is confirmed, authors can proceed to submit their RWS for approval. The submission includes a JSON file that lists all domains in the set, categorized by their relationship to the set primary. This categorization is crucial, as it dictates how browsers will handle cookie access for each domain.

The submission is made public, typically through a GitHub repository, to maintain transparency and allow for community scrutiny. This public accountability is a deterrent against misuse and ensures that the RWS aligns with the intended use cases, such as seamless sign-in across related properties or shared analytics.

After submission, the RWS undergoes a review process. If approved, browsers like Chrome will recognize the declared relationships and manage cross-domain cookie access accordingly. It's important to note that any changes to the set, such as adding or removing domains, require a resubmission and re-verification to maintain the integrity of the RWS.

In summary, setting up and submitting an RWS demands careful planning and adherence to technical guidelines to ensure a smooth experience for both site authors and users post third-party cookie deprecation.

The Role of Related Website Sets in Advertising and Conversion Tracking

In the evolving landscape of digital advertising, Related Website Sets (RWS) emerge as a pivotal element in the Privacy Sandbox initiative, particularly as we navigate the post-third-party cookie era. The RWS framework enables advertisers to maintain a semblance of continuity in tracking conversions and assessing campaign effectiveness without infringing on user privacy.

By allowing publishers to declare a network of related domains as part of a set, RWS facilitates the measurement of user interactions across these domains. This is crucial for advertisers who rely on conversion tracking to optimize their campaigns and allocate budgets effectively. Conversion tracking typically involves following a user's journey from an ad click to a desired action, such as a purchase or sign-up. In the absence of third-party cookies, this cross-domain tracking becomes a challenge.

RWS addresses this by permitting limited third-party cookie access within the declared set of related websites. Advertisers can thus attribute conversions to the correct source and gain insights into the performance of their ads across an organization's digital ecosystem. For instance, if a user clicks on an ad on brandx.com and later makes a purchase on brandx-shop.com, RWS ensures that this conversion is tracked within the same set, preserving the ability to measure ad effectiveness.

Importantly, RWS is not designed to be a tool for extensive user profiling or targeting. Instead, it strikes a balance between enabling essential advertising functions and upholding user privacy. Advertisers must adapt to this new paradigm, leveraging RWS for conversion tracking while exploring complementary Privacy Sandbox APIs for broader advertising needs.

Browser Compatibility: How Different Browsers Handle Related Website Sets

As the digital landscape evolves, browser vendors are tasked with the delicate balance of enhancing user privacy while maintaining a seamless web experience. Related Website Sets (RWS) is a pivotal concept within Google's Privacy Sandbox initiative, aimed at preserving user journeys without the reliance on third-party cookies. However, the approach to RWS is not uniform across all browsers, leading to a varied web experience.

Google Chrome, the progenitor of the RWS framework, is leading the charge by integrating this mechanism into its browser. Chrome uses RWS to allow a collection of related domains to share cookies in a controlled manner, thereby supporting cross-domain functionalities like single sign-on and preserving user preferences across affiliated sites.

Mozilla Firefox, while not directly implementing RWS, has employed similar principles through heuristic-based exceptions and storage access grants. Firefox's approach focuses on minimizing user disruption during navigation between related domains, albeit with a more conservative stance on cross-site cookie access.

Apple's Safari browser has historically taken a stringent stance on third-party cookies and tracking. Safari's Intelligent Tracking Prevention (ITP) heavily restricts cross-site tracking, and while it does not directly support RWS, it provides a form of site grouping through hard-coded exceptions for known affiliated domains.

Microsoft Edge, built on the same Chromium engine as Chrome, is expected to adopt a similar handling of RWS. However, the specifics of its implementation and the degree of alignment with Chrome's policies remain to be seen as the Privacy Sandbox initiative continues to evolve.

The landscape of browser compatibility for RWS is a testament to the ongoing dialogue between enhancing user privacy and maintaining the functional integrity of the web. As the Privacy Sandbox progresses, we can anticipate further developments and potential harmonization in how different browsers handle Related Website Sets.

Privacy Considerations: Balancing User Privacy with Site Functionality

Navigating the complex terrain of digital privacy, the concept of Related Website Sets (RWS) introduces a nuanced approach, ensuring the delicate harmony between safeguarding user privacy and the smooth operation of interconnected web domains. This innovative framework serves as the bedrock for RWS, with its sights set on enhancing the digital experience across a spectrum of related sites, all while staunchly protecting users' personal data.

RWS operates under a stringent framework, where site authors declare domain relationships, allowing browsers to judiciously manage cookie access. This framework is not a carte blanche for unfettered data sharing across sites; rather, it is a carefully calibrated mechanism designed to preserve user journeys that are essential for coherent site functionality. For instance, a user's sign-in state or shopping cart contents can persist across domain boundaries within a related set, ensuring a frictionless experience without the need for repeated authentications or loss of session data.

The implementation of RWS respects the user's expectation of privacy by default, with the browser acting as a gatekeeper, only granting cookie access when it aligns with the user's interactions and the declared site relationships. This approach mitigates the risk of tracking abuse, as the browser enforces limits on the number of domains that can be included in a set, and provides the option for user intervention when necessary.

Moreover, the public nature of RWS submissions fosters transparency and accountability, allowing for community scrutiny and the potential for reporting any misuse. As the digital ecosystem moves towards a cookie-less future, RWS stands as a testament to the possibility of achieving a harmonious blend of privacy and functionality, ensuring that user trust remains at the forefront of the web experience.

Future of Web Privacy: What Related Website Sets Mean for Users and Developers

The digital realm's landscape witnesses a transformative shift with the rollout of Related Website Sets (RWS) via Google's Privacy Sandbox. This move marks a significant stride towards redefining online privacy management. RWS emerges as a beacon for a fortified browsing environment, curtailing the pervasive influence of third-party cookies—a longstanding privacy adversary. This framework envisions a web where users enjoy reduced privacy infringements, enabled by a regulated ecosystem that confines data sharing to a consortium of verified sites.

Developers, on the other hand, are presented with a dual-edged sword. While RWS provides a framework to maintain site functionality in a post-third-party cookie era, it also imposes new challenges. Developers must now navigate the submission process, ensuring their related domains are correctly categorized within the set, and adapt to the limitations imposed by the subset definitions. The increased domain limit to five associated domains offers some flexibility, but it also requires careful consideration to ensure that the most critical domains are included within the set.

The future of web privacy is thus a balancing act. RWS aims to preserve user experience and site functionality while aligning with the broader privacy goals of the Privacy Sandbox. As this initiative moves forward, both users and developers will need to adapt to these changes. Users will benefit from increased transparency and control over their data, while developers will need to innovate within the constraints to provide seamless and secure online experiences. The dialogue between privacy and functionality continues, and RWS is a pivotal chapter in this ongoing narrative.

Conclusion: Related Website Sets

In the evolving landscape of digital privacy, Related Website Sets (RWS) emerge as a beacon for organizations navigating the imminent deprecation of third-party cookies. As part of Google's Privacy Sandbox initiative, RWS offers a structured method for companies to assert the kinship of their web domains, thereby preserving essential user experiences such as seamless sign-ins and personalized content across related sites. This mechanism strikes a delicate balance, aiming to maintain the functionality users have come to expect while bolstering their privacy on the web.

As we approach the timeline for cookie deprecation, RWS stands as a testament to the industry's adaptability and commitment to privacy. It's a solution that acknowledges the complexity of modern web ecosystems, providing a lifeline for legitimate cross-domain user journeys without compromising on the privacy-first ethos that is rapidly becoming the new standard. While the road ahead is paved with challenges and the need for widespread education, RWS is a crucial step toward a more private, yet still interconnected, web experience. As the digital community continues to dissect and implement this framework, it's clear that RWS is not just a stopgap but a forward-thinking approach to the cookieless future.


What are Related Website Sets (RWS)?

Related Website Sets is a mechanism within Google's Privacy Sandbox that allows companies to declare relationships among their websites. This enables browsers like Chrome to grant limited third-party cookie access for specific purposes, such as maintaining user sessions across different domains owned by the same entity.

How do Related Website Sets work?

Companies can create a collection of domains, with one designated as the "set primary" and others as "set members." These sets are submitted to the browser, which then uses the information to determine when to allow or deny third-party cookie access in a third-party context.

Why were Related Website Sets introduced?

As browsers move towards enhancing user privacy by blocking third-party cookies, RWS was introduced to minimize disruptions to user experiences that rely on cookies for functionality, such as staying signed in across multiple domains owned by the same company.

What is the difference between first-party and third-party cookies?

First-party cookies are set by the website you are visiting directly and are typically used to remember your settings and preferences. Third-party cookies are set by a website other than the one you are currently visiting, often used for tracking and advertising purposes.

Will Related Website Sets affect how ads are served?

RWS is not intended as an ads solution. For advertising use cases, developers should explore other Privacy Sandbox APIs like Topics, Protected Audience, and Attribution Reporting. RWS is primarily focused on preserving site functionality like single sign-on and shared preferences across related domains.

Can any domain be part of a Related Website Set?

No, only domains that have a declared and verifiable relationship with the primary domain can be part of a set. This is to prevent misuse and ensure that only legitimately related sites can share cookie access.

How many domains can be included in a Related Website Set?

The associated domain limit has been increased to five domains, plus one primary domain. For use cases requiring more than five associated domains, developers are encouraged to look into the Storage Access API (SAA) for solutions.

What happens if a website needs to change its Related Website Set?

If a website changes its set, certain transitions may require the browser to clear site data to prevent linking user identities across different sets. This is a security measure to maintain user privacy.

How can users know if they are browsing within a Related Website Set?

Browsers may provide UI elements that inform users about the Related Website Set a website belongs to. This transparency helps users understand the relationship between the sites they visit.

What's the timeline for the implementation of Related Website Sets?

The submission process for Related Website Sets is currently live, and developers can start creating and submitting their sets. The feature is expected to roll out in alignment with the broader Privacy Sandbox initiatives and the planned deprecation of third-party cookies in Chrome.

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