Client Hints are a set of HTTP request header fields for proactive content negotiation allowing clients to indicate a list of device and user-agent specific preferences.
Every time you visit this page, the server responds with this HTTP headers:
Response Headers sent by the Server
|Accept-CH||viewport-width, dpr, device-memory, rtt, downlink, ect, ua, platform, arch, model, mobile|
If you revisit browserleaks.com within 30 seconds, your browser should send HTTP Client Hints request headers:
ECT, and a set of User-Agent Client Hints request headers:
Client Hints received for the main document
Client Hints received for the iframe subrequest
Description of currently available HTTP Client Hints:
Viewport-Widthis the width of the user's viewport in CSS pixels.
DPR, short for Device Pixel Ratio, reports the ratio of physical pixels to CSS pixels of the user's screen.
Device-Memoryreveals the approximate amount of memory the current device has in GiB. Because this information could be used to fingerprint users, the value of
Device-Memoryis intentionally coarse. Valid values are
RTThint provides the approximate Round Trip Time, in milliseconds, on the application layer. The
RTThint, unlike transport layer RTT, includes server processing time. The value of
RTTis rounded to the nearest 25 milliseconds to prevent fingerprinting.
Downlinkhint, expressed in megabits per second (Mbps), reveals the approximate downstream speed of the user's connection. The value is rounded to the nearest multiple of 25 kilobits per second. Because again, fingerprinting.
ECThint stands for Effective Connection Type. Its value is one of an enumerated list of connection types, each of which describes a connection within specified ranges of both RTT and Downlink values. Valid values for
User-Agent Client Hints:
Sec-CH-UArepresents the user agent's brand and major version.
Sec-CH-UA-Platformrepresents the platform's brand and major version.
Sec-CH-UA-Archrepresents the underlying architecture's instruction set and width.
Sec-CH-UA-Modelrepresents the user agent's underlying device model.
Sec-CH-UA-Mobilerepresents whether the user agent should receive a specifically "mobile" UX.
- Privacy concerns raised about upcoming Client-Hints web standard — ZDNet
- Brave's Concerns with the Client-Hints Proposal — Brave Browser
- HTTP Client Hints — IETF
- Adapting to Users with Client Hints — Google Developers
- Automating Resource Selection with Client Hints — Google Developers