Preparing for the Deprecation of Third-Party Cookies: What Developers Need to Know



As we approach the end of an era for third-party cookies, developers must prepare their websites and applications for the upcoming changes. With Google Chrome planning to phase out third-party cookies for 100% of users by Q3 2024, subject to competition concerns being addressed, it's crucial for developers to understand the implications and take action to ensure a smooth transition. In this blog post, we'll explore what developers need to know about the deprecation of third-party cookies and the steps they can take to adapt their sites and services.

Understanding Third-Party Cookies

Third-party cookies have been a fundamental part of the web for nearly three decades, enabling functionality such as cross-site tracking, personalized advertising, and embedded content. However, they have also raised privacy concerns due to their ability to track user activity across different websites. As a result, browsers like Chrome are taking steps to phase out third-party cookies to enhance user privacy.

The Privacy Sandbox Initiative

To address the challenges posed by the removal of third-party cookies, Google has introduced the Privacy Sandbox initiative. This initiative aims to develop a set of APIs that provide alternative solutions for key use cases currently reliant on third-party cookies, such as advertising, measurement, and fraud prevention. These APIs are designed to preserve user privacy while still enabling essential functionality for websites and online services.

Preparing for the Deprecation

Developers should take the following steps to prepare for the deprecation of third-party cookies.

Audit Third-Party Cookie Usage

Start by auditing your website or application to identify instances where third-party cookies are being used. Look for cookies with the SameSite=None attribute, as these are the ones that will be affected by the deprecation. Chrome DevTools and the Privacy Sandbox Analysis Tool (PSAT) can help you identify and analyze third-party cookie usage.

Test for Breakage

Once you have identified the third-party cookies in use, test your site or application with third-party cookies disabled. Chrome provides a command-line flag (--test-third-party-cookie-phaseout) and a Chrome flag (chrome://flags/#test-third-party-cookie-phaseout) to simulate the state after the phase-out. Run your test suites or manually test critical user journeys to identify any breakages or issues that arise when third-party cookies are blocked.

Explore Alternative Solutions

For cross-site cookies that store data on a per-site basis, consider using the Partitioned attribute with the Cookies Having Independent Partitioned State (CHIPS) feature. This allows for separate cookie instances to be set per top-level site while maintaining user privacy. For cookies used across a small group of related sites, the Related Website Sets (RWS) feature can be used to allow cross-site access within the defined set of sites.

Migrate to Privacy-Preserving APIs

For other use cases that rely on third-party cookies, explore the privacy-preserving APIs provided by the Privacy Sandbox. These include APIs for federated identity (Federated Credential Management), anti-fraud and anti-spam (Private State Tokens), interest-based advertising (Topics), remarketing (Protected Audience), and ad measurement (Attribution Reporting). Evaluate which APIs are relevant to your use cases and start migrating your implementation accordingly.

Temporary Mitigation Options

While working on the necessary changes to migrate away from third-party cookies, there are temporary options available to preserve critical user experiences.

Third-Party Deprecation Trial

Chrome plans to offer a deprecation trial that allows third-party embeds to temporarily continue using third-party cookies for a limited period. This trial requires a review process and is intended for functions that greatly affect critical user journeys. Advertising use cases will not be considered for the deprecation trial.

Enterprise Controls

For enterprise-managed Chrome instances, administrators will have controls over the deprecation of third-party cookies. Enterprise administrators can set policies to temporarily allow third-party cookies while making the necessary changes to their sites and services.


The deprecation of third-party cookies is a significant milestone in the journey towards a more privacy-focused web. As developers, it's essential to understand the implications of this change and take proactive steps to ensure your websites and applications are prepared. By auditing your third-party cookie usage, testing for breakage, exploring alternative solutions, and migrating to privacy-preserving APIs, you can navigate this transition successfully.

Remember to stay updated with the latest developments and timelines provided by Chrome and the Privacy Sandbox initiative. If you encounter any issues or have questions, report them through the appropriate channels and engage with the developer community for support.

Embracing privacy-preserving technologies and adapting to the evolving web landscape is crucial for building trust with users and delivering secure and seamless online experiences. By taking action now, you can ensure your sites and services are ready for a future without third-party cookies.