Sec-CH-UA-Platform

Platform-aware content delivery is achieved through the Sec-CH-UA-Platform request header, a low-entropy client hint identifying the operating system by name.

Table of Contents

Usage

The Sec-CH-UA-Platform header is a low-entropy client hint sent by default in requests from supporting browsers. The header exposes basic platform information without requiring server opt-in through Accept-CH, making the data immediately available for adaptive content delivery.

Browsers send a quoted string indicating the platform name, such as "Windows", "macOS", "Android", or "Linux". This header works alongside Sec-CH-UA and Sec-CH-UA-Mobile as one of three low-entropy User-Agent Client Hints sent by default. Since Chrome's User-Agent reduction, the UA string freezes platform tokens to fixed values like Windows NT 10.0, making Sec-CH-UA-Platform the structured replacement for server-side platform detection.

Servers commonly use Sec-CH-UA-Platform to tailor interface elements to match platform conventions, adjust download links to offer the correct installer, or serve platform-specific instructions. The header enables content negotiation based on operating system without parsing complex User-Agent strings.

Values

Platform name

The value is a quoted string representing the operating system. Common values include:

  • "Windows" for Windows operating systems
  • "macOS" for Apple macOS
  • "Android" for Android devices
  • "Linux" for Linux-based systems
  • "Chrome OS" or "Chromium OS" for ChromeOS-family devices
  • "iOS" for Apple iOS
  • "Unknown" when the platform cannot be determined

The value is always enclosed in double quotes and sent as a Structured Fields String (sf-string).

Example

A browser running on Windows 11 sends the platform hint along with other low-entropy User-Agent client hints. The server receives platform information without requiring explicit opt-in.

Sec-CH-UA: "Not/A)Brand";v="8", "Chromium";v="130", "Google Chrome";v="130"
Sec-CH-UA-Mobile: ?0
Sec-CH-UA-Platform: "Windows"

A browser running on macOS sends the platform identifier for a Mac-based system. This enables the server to provide macOS-specific download links or styling.

Sec-CH-UA-Platform: "macOS"

An Android device identifies the platform, allowing the server to serve mobile-optimized resources or redirect to an app store.

Sec-CH-UA-Platform: "Android"

Crawlers and Sec-CH-UA-Platform

Verified crawler probe

Probe data from verified crawler traffic (September 2026 snapshot) shows which bots send Sec-CH-UA-Platform when requesting pages. Yes marks the header on at least nine of ten sampled requests from the bot, Sometimes marks a smaller share, and No marks absence.

Crawler Sends Sec-CH-UA-Platform
Amazonbot No
Applebot No
Baiduspider No
Bingbot No
ClaudeBot No
DuckDuckBot No
GPTBot No
Googlebot No
Googlebot (smartphone) No
Googlebot-Image No
Meta-ExternalAgent No
Meta-WebIndexer No
OAI-SearchBot No
SeznamBot No
YandexBot No
YandexFavicons No

See also

Last updated: September 21, 2026