The Impact of User-Agent Reduction and Client Hints on Privacy

The User-Agent (UA) reduction has the potential of being one of the most disruptive changes implemented by Google in recent years. Yes, it will impact user privacy, but how? Also, replacing the UA with User-Agent Client Hints will have direct implications for the Advertising and the Browser and Analytics industries. Let’s see why this is the case.

User Agent

The User Agent is a software that facilitates the interaction between the end user and the web content.

Typical User Agents would include web browsers, such as Google Chrome, Firefox or Safari, or media players and plug-ins. These, when interacting with web content, usually set a User-Agent header in every HTTP request containing a string that allows for web applications to gather some information about the end user: the application / browser and its version, the operating system, and the vendor.

Today, the information gathered from the UA string is used by many web applications to provide a more curated version of their services. When talking more specifically about the Digital Advertising industry, such details are used for providing a more segmented targeting, helping to place ads where they are more relevant.

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Below you will find how an HTTP call is working today.

What is the User-Agent Reduction

The User-Agent (UA) string reduction is a process started by Google that aims to reduce the information found in a typical UA string, with the goal to reduce or even block the passive fingerprinting of the end user.

With today’s structure of the UA string, there is a certain degree of detail that web applications can leverage to passively fingerprint the user. The core problem is that this can be done without any consent, or even awareness, of the end user, and, at the same time, the user is not given the chance to opt-out. The reduced UA string will only include the browser’s name and significant version, the type of device the request came from (desktop vs mobile), and the platform (e.g.: Windows, macOS, etc). To access more data, the web application will need to request it through User Agent Client Hints (UA-CH).

Client Hints

The User Agent Client Hints are a mechanism that allows web applications to request more detailed information about the user, essentially giving access to the same information that is being removed from the UA string. The key difference, however, is the need for an explicit request for the User Agent to send these extra details, making the User Agent aware that the web application will be using it.

As you will see below, the process of leveraging from UA-CH is slightly more complex than the existing one relying on UA header, containing an added step before the actual content is rendered to the end user.

Timeline

Google rolled out the User Agent Client Hints in March 2021 and started the UA String reduction in April 2022, with the aim to having it fully implemented by February 2023:

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The Impact of User-Agent Reduction

This change, currently driven by Google, has a few different pros and cons associated with it. On the positive side it should help with reducing privacy concerns for the end user, and also sending only the data that is truly relevant for the web application in a well formatted way. On the other hand, it is not a widely accepted standard yet, therefore it is not supported by all browsers. Furthermore, it increases response latency due to the extra call required and can only be sent over secure connections.

Such a move will have a serious impact on many companies that will have to adapt their software to the new standard so that they can continue to provide the same quality of service to their clients. As an example, within the Digital Advertising industry, the impact will be seen on a simple ad request with an increased latency for ad delivery and also on many existing programmatic integrations between different networks and partners.

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Conclusion

The User-Agent reduction and introduction of the User Agent Client Hints appears to be a step towards an increased user privacy, by giving more control over what information is shared with the web applications. However, as of today, not all browsers still support User Agent Client Hints, and while Google Chrome represents a big chunk of the internet users with a whooping 60%+ share, other browsers like Safari (19%) and Firefox (3%) do reflect a significant share of the overall internet accesses. This will lead web application developers to having to support both the “old” and the “new” approaches.