User-Agent Client Hints Explained: The Replacement for the UA String

Q: What are User-Agent Client Hints?

User-Agent Client Hints are a Chromium mechanism that replaces the old User-Agent string with structured data shared through HTTP headers and a JavaScript API called navigator.userAgentData. Basic, low-entropy details are sent by default, while more granular details must be explicitly requested by the website. The goal is to reduce the amount of device information broadcast automatically to every site.

Q: How are Client Hints different from the old User-Agent string?

The old User-Agent string was sent automatically on every request and revealed a lot of detail to all sites by default. Client Hints split that information into low-entropy hints sent by default and high-entropy hints that a server must specifically ask for. This makes access to granular data more deliberate and observable rather than passive.

Q: Do Client Hints stop fingerprinting?

No. They reduce the data sent by default, but a site can still request the high-entropy hints and obtain detailed information about your device. The privacy benefit is that this access is now explicit and observable rather than automatic. Fingerprinting entropy is moved and made more visible, not removed.

Q: What is the difference between low-entropy and high-entropy Client Hints?

Low-entropy hints reveal little and are sent by default, such as the browser brand, a mobile flag, and the platform name. High-entropy hints reveal more, such as the platform version, CPU architecture, and device model, and are only sent when a server requests them with the Accept-CH header. The split exists to limit how much detail is shared without a deliberate request.

Q: Which browsers use User-Agent Client Hints?

User-Agent Client Hints are a Chromium feature, so they are used by Chrome, Edge, and other Chromium-based browsers. Firefox and Safari have generally not adopted the mechanism and handle the User-Agent string differently. Because of this, the way device information is exposed can differ depending on the browser you use.

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The Quiet Replacement for the User-Agent String
For decades, every request your browser made carried a User-Agent string that told the server your browser, version, and operating system. User-Agent Client Hints are the Chromium mechanism designed to replace that always-broadcast string with a structured, on-request system. See exactly what your browser sends today with our user agent tool. This page sits alongside the browser fingerprinting overview, because how device data is shared is central to fingerprinting.
Why the Change Happened
The old User-Agent string broadcast a lot of detail to every server on every request, automatically, which added passive fingerprinting entropy. Chromium has been reducing and freezing that string and shifting the detail into Client Hints, which are sent more deliberately. The hints exist both as HTTP request headers and as a JavaScript API called navigator.userAgentData.
Low-Entropy Hints
Low-entropy hints reveal little and are sent by default, because on their own they do not narrow you down much. They include Sec-CH-UA for the browser brand and major version, Sec-CH-UA-Mobile as a simple mobile flag, and Sec-CH-UA-Platform for the operating system name such as Windows or Android.
High-Entropy Hints
High-entropy hints reveal more and are not sent by default. A server must explicitly ask for them. Examples include Sec-CH-UA-Platform-Version, Sec-CH-UA-Arch for CPU architecture, Sec-CH-UA-Model for device model, and Sec-CH-UA-Full-Version-List. The server advertises which hints it wants with the Accept-CH response header, and JavaScript can read them through navigator.userAgentData.getHighEntropyValues.
What It Means for Privacy
The honest take: this is not a privacy guarantee. It moves granular device data from being passively broadcast to being actively requested, which makes high-entropy access more visible and more controllable in principle. But a site that wants the detail can simply request it, so the same entropy is still obtainable. The change is about reduced default exposure and better observability, not the removal of fingerprinting. It pairs with covert vectors like canvas and TLS fingerprinting, and you can see your full picture in a privacy checkup.
Which Browsers Use It
User-Agent Client Hints are a Chromium feature, so they are used by Chrome, Edge, and other Chromium-based browsers. Firefox and Safari have generally not adopted the mechanism and handle the User-Agent string differently, so how your device information is exposed can depend on the browser you use.
Frequently Asked Questions
What are User-Agent Client Hints?
User-Agent Client Hints are a Chromium mechanism that replaces the old User-Agent string with structured data shared through HTTP headers and a JavaScript API called navigator.userAgentData. Basic, low-entropy details are sent by default, while more granular details must be explicitly requested by the website. The goal is to reduce the amount of device information broadcast automatically to every site.
How are Client Hints different from the old User-Agent string?
The old User-Agent string was sent automatically on every request and revealed a lot of detail to all sites by default. Client Hints split that information into low-entropy hints sent by default and high-entropy hints that a server must specifically ask for. This makes access to granular data more deliberate and observable rather than passive.
Do Client Hints stop fingerprinting?
No. They reduce the data sent by default, but a site can still request the high-entropy hints and obtain detailed information about your device. The privacy benefit is that this access is now explicit and observable rather than automatic. Fingerprinting entropy is moved and made more visible, not removed.
What is the difference between low-entropy and high-entropy Client Hints?
Low-entropy hints reveal little and are sent by default, such as the browser brand, a mobile flag, and the platform name. High-entropy hints reveal more, such as the platform version, CPU architecture, and device model, and are only sent when a server requests them with the Accept-CH header. The split exists to limit how much detail is shared without a deliberate request.
Which browsers use User-Agent Client Hints?
User-Agent Client Hints are a Chromium feature, so they are used by Chrome, Edge, and other Chromium-based browsers. Firefox and Safari have generally not adopted the mechanism and handle the User-Agent string differently. Because of this, the way device information is exposed can differ depending on the browser you use.
Last updated: April 2026