When Internet users visit a web site, a text , and language. Bot s, such as web crawlers, often also include a URL and/or E-mail Address so that the Webmaster can contact the operator of the bot.
The user-agent string is one of the criteria by which crawlers can be excluded from certain pages or parts of a website using the " Robots Exclusion Standard " (''robots.txt''). This allows webmasters who feel that certain parts of their website should not be included in the data gathered by a particular crawler, or that a particular crawler is using up too much Bandwidth , to request that crawler not to visit those pages.
At various points in its history, use of the Web has been dominated by one browser to the extent that many websites are designed to work with that particular browser, rather than according to standards from bodies such as the W3C and IETF . Such sites often include "browser sniffing" code, which alters the information sent out depending on the User-Agent string received. This can mean that less popular browsers are not sent complex content, even though they might be able to deal with it correctly, or in extreme cases refused ''all'' content. Thus various browsers "cloak" or "spoof" this string, in order to identify themselves as something else to such detection code; often, the browser's real identity is then included later in the string.
The earliest example of this is Internet Explorer 's use of a User-Agent string beginning "Mozilla/ (compatible; MSIE ...", in order to receive content intended for Netscape Navigator , its main rival at the time of its development. It should be stressed that this is ''not'' a reference to the open-source Mozilla browser, which was developed much later, but to the original codename for Navigator, which was also the name of The Netscape Company Mascot . This format of User-Agent string has since been copied by other user agents, partly because Explorer, in turn, came to dominate.
When Internet Explorer became the dominant web browser, rivals such as Firefox , Safari , and Opera implemented systems whereby the user could select a false User-Agent string to send, such as that of a recent version of Explorer. Some – e.g. Firefox and Safari – duplicate the User-Agent string they are trying to spoof exactly; others – e.g. Opera – duplicate the User-Agent string but add the genuine browser name to the end. This latter approach, of course, leads to a string containing three names and versions: first, the user agent claims to be "Mozilla" (i.e. Netscape Navigator); then, "MSIE" (Internet Explorer); and finally, the actual browser, such as "Opera".
Beside browsers, other programs utilizing HTTP protocol, like most Download Manager s and Offline Browser s, also had the ability to change the user agent string sent to servers to user's liking. This is presumably done in an effort to maintain compatibility with certain servers (some servers refused to serve those programs right away because they are mostly used carelessly, thus burdening the server).
This Vicious Circle is expected to continue in the area of web browsers. Some standards-based web developers have started the " Viewable With Any Browser " campaign which encourages developers to design webpages according to official standards, not for any particular browser(s).
As Of 2005 , many websites are more standards-compliant than at other times in the history of the web. However, out-dated JavaScript , which effectively locks out browsers other than Explorer or Navigator, is still in use - especially on smaller, non-corporate, websites. This is often blamed on use of Voodoo Programming , in the form of Copying And Pasting older code without actually understanding what effect this will have on the website.
One result of user agent spoofing is that the Usage Share of Internet Explorer, the user agent browsers typically spoof, is probably overestimated, and the usage share of all other browsers may be underestimated.
The term refers to websites that show different content when viewed with a certain user agent. On the Internet, this will result in a different site being shown when browsing the page with a specific browser (e.g. Microsoft Internet Explorer). A famous example of this is Microsoft 's Outlook 2003 Web Access. When viewed with IE, much more functionality is displayed compared to the same page in any other browser. User agent sniffing is mostly considered poor practice, since it encourages browser specific design. Many webmasters are recommended to create a HTML markup that is as standardised as possible, to allow correct rendering in as many browsers as possible.
Websites specifically targeted towards mobile phones, like NTT DoCoMo 's I-Mode or Vodafone 's Vodafone Live! portals, often rely heavily on user agent sniffing, since browsers on mobile phones often differ a lot from each other. Many developments in mobile browsing have been made in the last few years, while many older phones that do not possess these new technologies are still heavily used. Therefore, mobile webportals will often generate completely different markup code depending on the mobile phone used to browse them. These differences can be small (e.g. resizing of certain images to fit smaller screens), or quite extensive (e.g. rendering of the page in WML instead of XHTML ).
- Internet Explorer versions:
- ---1.0 on Windows 95 — Microsoft Internet Explorer/4.0b1 (Windows 95)
- ---1.5 on Windows NT — Mozilla/1.22 (compatible; MSIE 1.5; Windows NT)
- ---2.0 on Windows 95 — Mozilla/1.22 (compatible; MSIE 2.0; Windows 95)
- ---3.01 on Windows 98 — Mozilla/2.0 (compatible; MSIE 3.01; Windows 98)
- ---5.0 on SunOS — Mozilla/4.0 (compatible; MSIE 5.0; SunOS 5.9 sun4u; X11)
- ---5.1.7 on Mac OS 9 — Mozilla/4.0 (compatible; MSIE 5.17; Mac_PowerPC)
- ---5.2.3 on Mac OS X — Mozilla/4.0 (compatible; MSIE 5.23; Mac_PowerPC)
- ---5.5 on Windows 2000 — Mozilla/4.0 (compatible; MSIE 5.5; Windows NT 5.0)
- ---6.0 in MSN 2.5 on Windows 98 — Mozilla/4.0 (compatible; MSIE 6.0; MSN 2.5; Windows 98)
- ---6.0 on Windows XP SP2 — Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)
- ---6.0 on Windows XP SP2 with .NET Framework 1.1 installed — Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322)
- ---6.0 on Windows XP Media Center Edition 2005 with .NET Framework 1.0, 1.1, and 2.0 installed— Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.0.3705; .NET CLR 1.1.4322; Media Center PC 4.0; .NET CLR 2.0.50727)
- ---6.0 on Windows Server 2003 Service Pack 1 with .NET Framework 1.1 installed — Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; SV1; .NET CLR 1.1.4322)
- ---7.0 beta running on Windows XP — Mozilla/4.0 (compatible; MSIE 7.0b; Windows NT 5.1)
- ---7.0 beta 1 running on Windows XP — Mozilla/4.0 (compatible; MSIE 7.0b; Win32)
- ---7.0 beta running on Windows Vista — Mozilla/4.0 (compatible; MSIE 7.0b; Windows NT 6.0)
- Pocket Internet Explorer versions:
- ---Microsoft Pocket Internet Explorer/0.6 - PIE 1.0, seems that they forgot to change it to 1.0.
- ---Mozilla/1.1 (compatible; MSPIE 2.0; Windows CE) - PIE 2.0
- ---On Windows Mobile 2003 — Mozilla/4.0 (compatible; MSIE 4.01; Windows CE; PPC; 240x320)
- ---On Windows Mobile 2003 Second Edition, running on a Motorola MPx220 Smartphone — MOT-MPx220/1.400 Mozilla/4.0 (compatible; MSIE 4.01; Windows CE; Smartphone; 176x220)
- AOL Explorer versions (not classic AOL 8.0, 9.0) (adds "America Online Browser X.X;"):
- ---1.1 — Mozilla/4.0 (compatible; MSIE 6.0; America Online Browser 1.1; rev1.1; Windows NT 5.1;)
- ---1.2 — Mozilla/4.0 (compatible; MSIE 6.0; America Online Browser 1.1; rev1.2; Windows NT 5.1;)
- ---1.5 — Mozilla/4.0 (compatible; MSIE 6.0; America Online Browser 1.1; rev1.5; Windows NT 5.1;)
- Avant Browser versions:
- ---Ancient version — Advanced Browser (http://www.avantbrowser.com)
- ---Old version — Avant Browser (http://www.avantbrowser.com)
- ---More current — Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; Avant Browser {Link without Title} ; iOpus-I-M; QXW03416; .NET CLR 1.1.4322)
- Konqueror versions:
- ---3.1-RC1 — Mozilla/5.0 (compatible; Konqueror/3.1-rc3; i686 Linux; 20020515)
- ---3.1 (French) — Mozilla/5.0 (compatible; Konqueror/3.1; Linux 2.4.22-10mdk; X11; i686; fr, fr_FR)
- Minimo :
- ---0.007 on Windows Mobile 2003 — Mozilla/5.0 (Windows; U; Windows CE 4.21; rv:1.8b4) Gecko/20050720 Minimo/0.007
- Mozilla :
- --- 1.7.8 on Linux — Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.8) Gecko/20050511
- --- 1.7.12 on Gentoo Linux — Mozilla/5.0 (X11; U; Linux i686; cs-CZ; rv:1.7.12) Gecko/20050929
- Mozilla Firefox versions:
- ---1.0 (Dutch) on Windows XP — Mozilla/5.0 (Windows; U; Windows NT 5.1; nl-NL; rv:1.7.5) Gecko/20041202 Firefox/1.0
- ---1.0.4 on Ubuntu Linux , on AMD64 — Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.7.6) Gecko/20050512 Firefox
- ---1.0.4 on FreeBSD 5.4 on I386 — Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.8) Gecko/20050609 Firefox/1.0.4
- ---1.0.5 on Slackware — Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.9) Gecko/20050711 Firefox/1.0.5
- ---1.0.6 on Windows XP — Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.10) Gecko/20050716 Firefox/1.0.6
- ---1.0.6 on Mac OS X 10.4 PPC — Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-GB; rv:1.7.10) Gecko/20050717 Firefox/1.0.6
- ---1.0.7 on Windows XP — Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.12) Gecko/20050915 Firefox/1.0.7
- ---1.0.7 on Mac OS X 10.3 PPC — Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.7.12) Gecko/20050915 Firefox/1.0.7
- ---1.5b1 on Windows XP — Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8b4) Gecko/20050908 Firefox/1.4
- ---1.5b1 on Mac OS X 10.3 PPC — Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.8b4) Gecko/20050908 Firefox/1.4
- ---1.5 on Windows XP — Mozilla/5.0 (Windows; U; Windows NT 5.1; nl; rv:1.8) Gecko/20051107 Firefox/1.5
- ---1.5.0.1 on Windows XP — Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.8.0.1) Gecko/20060111 Firefox/1.5.0.1
- ---1.5.0.1 on Windows Vista — Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.8.0.1) Gecko/20060111 Firefox/1.5.0.1
- ---1.5.0.2 on Ubuntu Linux — Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.0.2) Gecko/20060308 Firefox/1.5.0.2
- ---2.0a1 on Windows XP — Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8) Gecko/20060321 Firefox/2.0a1
- SeaMonkey versions:
- ---1.0b on Windows XP — Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8) Gecko/20051219 SeaMonkey/1.0b
- ---1.0 on Windows 98 — Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.8.0.1) Gecko/20060130 SeaMonkey/1.0
- Netscape versions (based on non-proprietary shared Mozilla code base):
- ---6.1 on Windows 2000 — Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:0.9.2) Gecko/20020508 Netscape6/6.1
- ---7 on Sun Solaris 8 — Mozilla/5.0 (X11; U; SunOS sun4u; en-US; rv:1.0.1) Gecko/20020920 Netscape/7.0
- ---7.1 on Windows XP — Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax)
- ---8.0.1 on Windows XP using Gecko — Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.5) Gecko/20050519 Netscape/8.0.1
- ---8.0.1 on Windows XP using MSHTML (with .NET installed) — Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50215) Netscape/8.0.1
- ---8.1 on Windows XP using Gecko (with .NET installed) — Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.5) Gecko/20060127 Netscape/8.1
- OmniWeb versions:
- ---5.1.1 (v563.51) on Mac OS X — Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en-US) AppleWebKit/125.4 (KHTML, like Gecko, Safari) OmniWeb/v563.51
- ---5.1.2 beta 1 (v563.57) on Mac OS X — Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en-US) AppleWebKit/125.4 (KHTML, like Gecko, Safari) OmniWeb/v563.57
- Safari versions:
- ---v125 on Mac OS X — Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en) AppleWebKit/124 (KHTML, like Gecko) Safari/125
- ---v125 on Mac OS X , cloaked as MSIE — Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2)
- ---v312 on Mac OS X — Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en-us) AppleWebKit/312.1 (KHTML, like Gecko) Safari/312
- ---2.0 (v412) on Mac OS X — Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en-us) AppleWebKit/412 (KHTML, like Gecko) Safari/412
- WebExplorer (based on Mosaic ):
- ---1.1h on OS/2 , an old HTTP/1.0 UA — IBM-WebExplorer-DLL/v1.1h
- Camino :
- ---1.0b1 on Mac OS X — Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en-US; rv:1.8) Gecko/20051107 Camino/1.0b1
- ---1.0 on Mac OS X — Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.8.0.1) Gecko/20060214 Camino/1.0
- ELinks 0.4pre5 on Linux — ELinks (0.4pre5; Linux 2.4.27 i686; 80x25)
- Links versions:
- ---0.99pre14 under Cygwin on Windows 2000 — Links (0.99pre14; CYGWIN_NT-5.0 1.5.16(0.128/4/2) i686; 80x25)
- ---2.1pre17 under Gentoo Linux — Links (2.1pre17; Linux 2.6.11-gentoo-r8 i686; 80x24)
- ---2.1pre19 under Gentoo Linux using X Window System — Links (2.1pre19; Linux 2.6.14-gentoo-r5 i686; x)
- Lynx 2.8.4rel.1 on Linux — Lynx/2.8.4rel.1 libwww-FM/2.14
- Off By One 3.5a on Windows XP — Mozilla/4.7 (compatible; OffByOne; Windows 2000)
- W3m on FreeBSD — w3m/0.5.1
''Version'' '''('''''Platform''''')'''
Where:
- ''Version'': Windows version because IE was originally supposed to be included with Windows 95, e.g.: for Internet Explorer 1.0 beta
- ''Platform'': operating system, e.g.:
Where:
- ''MozVer'': Netscape compatibility version
- --- : Internet Explorer 1.5 and 2.0
- --- : Internet Explorer 3.x for Windows and Internet Explorer 2.1 for Mac
- --- : Internet Explorer 3.x for Mac
- --- : Internet Explorer 4.x and higher
- ''IEVer'': Internet Explorer version number, e.g.: , '''3.01''', '''5.0b1'''
- ''Provider'': Access provider, e.g.:
- --- ''Version''
- ---
- ''Platform'': Operating system
- --- (including Windows NT 3.x)
- ---
- ---
- --- : Windows Millennium Edition (Windows Me)
- ---
- ---
- --- : Windows 2000
- --- : Windows 2000, Service Pack 1 (SP1)
- --- : Windows XP
- --- : Windows Server 2003
- --- : Windows Vista
- --- : Windows CE and Windows Mobile
- ---
- --- : Used up until IE 4.x
- --- Used from IE 5.x and up
- ''Extension'': optional, a list of semicolon-seperated extensions installed, e.g.:
- --- ''Version'': .NET Framework common language runtime installed
- --- : Internet Explorer 6 in Windows XP SP2 and Windows Server 2003 SP1 installed
- --- : Pocket PC
- --- ''Version'': Tablet services are installed
- --- : 64-bit Windows
- --- : Intel Itanium processor
- --- : x64 processor
- --- : x64 processor
- --- : 32-bit Internet Explorer is running on 64-bit Windows
- --- ''Version'': Windows MCE, where ''Version'' is:
-- : Media Center 2004
-- : Media Center 2005
-- : Media Center 2005 with update rollup 1
-- : Media Center 2005 with update rollup 2
- --- ''Version'': browsing from within Media Center interface
- --- : MSIE retrieving pages for Offline Content feature
- --- Various 3rd party extensions, like: ''Version''''')''' (RealPlayer webbrowser), '''Alexa Toolbar''', '''Maxthon''', '''Crazy Browser''' ''Version'', '''MyIE2''', '''Avant Browser {Link without Title} '''
- ''Addition''
- --- ''Version'': Netscape using MSHTML rendering engine
''This only applies to earlier versions of Netscape. Netscape 6.0 or higher based on the Gecko engine should see the Mozilla section below''
''Version'' ['''['''''Language''''' '''] '''('''''Platform''''';''' ''Security''[''';''' ''SubPlatform'' [''StandAlone'']''')'''
Where:
- ''Version'': version number
- : includes HTML editor
- ''Language'': standarized two-letter language identifier, e.g.: , '''fr''', '''es''' (Netscape 2.x and 3.x: only for non-english versions, Netscape 4.x: not on Macintosh platforms?)
- ''Provider'', may contain variants of ( Client Customization Kit and Mission Control Desktop , for ISPs and OEMs)
- ''Platform''
- --- : Windows 3.x
- --- : Windows 95, where ''SubPlatform'' can be:
-- for 16-bit version of Netscape
- --- : Windows 98
- --- : Windows NT 3.x
- --- : Windows 2000
- --- : Windows XP
- --- , where ''SubPlatform'' is:
-- ''Distribution'' ''Version'' {Link without Title} , e.g.: , '''SunOS 5.6 sun4u''', '''IRIX 6.5 IP32'''
- --- , where ''SubPlatform'' is:
--
--
- ''Security''
- --- : strong security (USA)
- --- : weak security (International)
- --- : no security
- ''StandAlone'': standalone Navigator is indicated by (X11 platforms), ''';Nav''' (Windows, note missing space) or ''', Nav''' (on Macintosh), only for version 4.x
- ''') Gecko/'''''GeckVer'' [''Product'''''/'''''ProdVer'']
Where:
- ''MozVer'': Netscape compatibility version
- --- for all known Mozilla browsers
- ''Platform'' and ''SubPlatform''
- ---
-- : Windows 3.11
-- : Windows 95
-- : Windows 98
-- : Windows Me
-- : Windows NT 3.51
-- : Windows NT 4.0
-- : Windows 2000
-- : Windows XP (except XP Professional x64 Edition)
-- : Windows Server 2003 and Windows XP Professional x64 Edition
-- : Windows Mobile 2003
- ---
--
--
--
- ---
-- {Link without Title} ''Hardware''
-- ''Hardware''
-- ''Hardware''
--
- ''Security''
- --- : strong security (USA)
- --- : weak security (International)
- --- : no security
- ''Language'': standarized language identifier, e.g.: , '''en-US''', '''en-GB'''
- ''Revision'': e.g. , '''1.0rc3''', '''1.7.8''', '''1.8a2'''
- ''Extension''
- --- ''Version''
- ''GeckVer'': Gecko (layout engine) compilation date, in the format ''YYYYMMDD''
- ''Product''
- --- , '''Netscape6'''
- --- , '''Firebird''', '''Firefox'''
- ---
- ---
- ---
- ---
- ''ProdVer'': Product version
Netscape , Mozilla , Opera and some others use one of these three letters to specify the browser's Encryption strength. Since the US government wouldn't allow encryption higher than 40-bit to be exported from the USA, different versions were released with different encryption strengths. "U" stands for "USA" (for the version with 128-bit encryption), "I" stands for "International" (the browser has 40-bit encryption and can be used anywhere in the world), "N" stands for "None" (no encryption). Originally the "U" version was allowed for download only from the USA, but since then the US government has loosened its policy and exporting high encryption is now permitted to most countries (see '' Export Of Cryptography '' for more information). Now Netscape and Mozilla distribute their browsers only in a "U" version, since an international version is no longer required.
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