Chromium Blog: UA String Changes Coming In Chrome 11

Chromium Blog

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UA String Changes Coming In Chrome 11

Thursday, March 31, 2011

Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US) AppleWebKit/534.16 (KHTML, like Gecko) Chrome/10.0.648.204 Safari/534.16

Mozilla/5.0 (X11; U; Linux x86_64; en-US) AppleWebKit/534.16 (KHTML, like Gecko) Chrome/10.0.648.204 Safari/534.16Mozilla/5.0 (Windows NT 6.0; WOW64) AppleWebKit/534.24 (KHTML, like Gecko) Chrome/11.0.696.16 Safari/534.24

Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/534.24 (KHTML, like Gecko) Chrome/11.0.696.16 Safari/534.24

On Windows, the initial "Windows;" platform identifier has been removed. This was redundant with the subsequent OS version identifier, and makes us more compatible with Internet Explorer, whose UA string doesn't have this initial token.

The "U" SSL encryption strength token has been removed. This token dates from more than a decade ago, when U.S. export laws limited the encryption strength that could be built into software shipped to various other countries; the valid values are "U" (for "USA" 128-bit encryption support), "I" (for "International" 40-bit encryption support), and "N" (for "None", no encryption support). These days, every browser ships with 128-bit SSL support everywhere, so it's not necessary to advertise it.

On 64-bit versions of Windows, tokens have been added after the OS version. For 32-bit Chrome builds running on 64-bit Windows, we've added "WOW64". (WOW64" stands for "Windows 32-bit On Windows 64-bit" and is the name Microsoft gives its 32-bit compatibility subsystem.) In our source code, we've also added identifiers for 64-bit native builds, specifically "Win64; x64" for x64-based processors and "Win64; IA64" for Itanium systems. (However, we don't currently ship such builds, or have any immediate plans to.) These tokens are useful for sites that need to provide download links for native executables, and match what Internet Explorer uses.

The locale has been removed. Web authors who want to know what languages a browser supports should use the HTTP Accept-Language header instead, which can supply multiple locales. In fact, websites that relied on the UA string locale probably had some very unhappy visitors, because Chrome always had a bug where the UA string locale was reported as "en-US", regardless of the user's desired locale(s)!

http://hacks.mozilla.org/2010/09/final-user-agent-string-for-firefox-4/--user-agent="<Put older UA string here>"about:http://crbug.com/
Posted by Peter Kasting, Software Engineer

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