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Encyclopedia > User Agent

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A user agent is the client application used with a particular network protocol; the phrase is most commonly used in reference to those which access the World Wide Web, but other systems such as SIP uses the term user agent to refer to the user's phone. Web user agents range from web browsers to search engine crawlers ("spiders"), as well as mobile phones, screen readers and braille browsers used by people with disabilities. When Internet users visit a web site, a text string is generally sent to identify the user agent to the server. This forms part of the HTTP request, prefixed with User-agent: or User-Agent: and typically includes information such as the application name, version, host operating system, and language. Bots, 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. Image File history File links Broom_icon. ... In computing, a client is a system that accesses a (remote) service on another computer by some kind of network. ... In networking, a communications protocol or network protocol is the specification of a set of rules for a particular type of communication. ... WWWs historical logo designed by Robert Cailliau The World Wide Web (commonly shortened to the Web) is a system of interlinked, hypertext documents accessed via the Internet. ... The Session Initiation Protocol (SIP) is an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. ... An example of a Web browser (Internet Explorer 7) A Web browser is a software application that enables a user to display and interact with text, images, and other information typically located on a Web page at a website on the World Wide Web or a local area network. ... This article is about search engines. ... A web crawler (also known as a Web spider or Web robot) is a program or automated script which browses the World Wide Web in a methodical, automated manner. ... A screen reader is a software application that attempts to identify and interpret what is being displayed on the screen. ... Braille code where the word (, French for first) can be read. ... In computer programming and formal language theory, (and other branches of mathematics), a string is an ordered sequence of symbols. ... The inside/front of a Dell PowerEdge web server The term Web server can mean one of two things: A computer program that is responsible for accepting HTTP requests from clients, which are known as Web browsers, and serving them HTTP responses along with optional data contents, which usually are... Hypertext Transfer Protocol (HTTP) is a communications protocol used to transfer or convey information on the World Wide Web. ... // An operating system (OS) is the software that manages the sharing of the resources of a computer. ... Internet bots, also known as web robots, WWW robots or simply bots, are software applications that run automated tasks over the internet. ... “URL” redirects here. ... An -mail address identifies a location to which e-mail messages can be delivered. ... A webmaster is a person responsible for designing, developing, marketing, or maintaining Web site(s). ...

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. The robots exclusion standard or robots. ... -1...


User agent spoofing

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 World Wide Web Consortium (W3C) is a consortium that produces standards—recommendations, as they call them—for the World Wide Web. ... The Internet Engineering Task Force (IETF) is charged with developing and promoting Internet standards. ...

The earliest example of this is Internet Explorer's use of a User-Agent string beginning "Mozilla/<version> (compatible; MSIE <version>...", 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. Windows Internet Explorer (formerly Microsoft Internet Explorer, abbreviated MSIE), commonly abbreviated to IE, is a series of proprietary graphical web browsers developed by Microsoft and included as part of the Microsoft Windows line of operating systems starting in 1995. ... Netscape Navigator, also known as Netscape, was a proprietary web browser that was popular during the 1990s. ... Mozilla was the official, public, original name of Mozilla Application Suite by the Mozilla Foundation, nowadays called SeaMonkey suite. ... Mozilla was the mascot of the now disbanded Netscape Communications Corporation. ...

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". Opera also offers a full masking as Internet Explorer or Firefox, which hides "Opera" completely. Mozilla Firefox is a graphical web browser developed by the Mozilla Corporation, and a large community of external contributors. ... Safari is a web browser developed by Apple Inc. ... Opera is an Internet suite which handles common internet-related tasks, including visiting web sites, sending and receiving e-mail messages, managing contacts, and online chat. ...

Beside browsers, other programs utilizing HTTP protocol, like most download managers and offline browsers, 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). A download manager is a computer program designed to download files from the Internet, unlike a web browser, which is mainly intended to browse webpages on the World Wide Web (with file downloading being of secondary importance). ... Many modern web browsers have a mode entitled offline browsing, where links to webpages are redirected to local copies in a temporary folder. ...

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). In many parts of economics there is an assumption that a complex system of determinants will tend to lead to a state of equilibrium. ... Viewable With Any Browser is a campaign to encourage web developers to create websites that are interoperable with any web browsers. ...

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 on many websites.[original research?] This is often blamed on use of cargo cult programming, in the form of copying and pasting older code without actually understanding what effect this will have on the website. Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... It has been suggested that Client-side JavaScript be merged into this article or section. ... Cargo cult programming is an incompetent style of computer programming characterized by the ritual inclusion of code or program structures that serve no real purpose. ... Copy and paste programming is an informal computer programming style that simply copies code from one program to another. ...

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 other browsers may be underestimated. User agent spoofing can also provide a security issue by spoofing search engine bots and bypassing key parts in a website. A rough estimation of usage share of layout engines/web browsers This article aims to be an unbiased historical record for the usage share of web browsers, based on statistics and articles published by well-known websites. ...

User agent sniffing

The term user agent sniffing 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). An infamous 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 for Web 2.0 web sites, since it encourages browser specific design. Many webmasters are recommended to create an HTML markup that is as standardised as possible, to allow correct rendering in as many browsers as possible. Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... Microsoft Outlook is a personal information manager from Microsoft, and is part of the Microsoft Office suite. ... In the analysis and promotion of web-technology, the phrase Web 2. ...

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). NTT DoCoMo, Inc. ... NTT DoCoMos i-mode is a wireless Internet service popular in Japan and is increasing in popularity in other parts of the world, such as the Israel (Cellcom being the main company to sell i-mode phones and service there). ... Vodafone Group Plc is a mobile network operator headquartered in Newbury, Berkshire, England, UK. It is the largest mobile telecommunications network company in the world by turnover and has a market value of about £84. ... Vodafone live!™ is the brand name for the multimedia portal service of mobile phone operator Vodafone, which was initially developed by Japans J-Phone under the J-Sky brand. ... Wireless Markup Language is the primary content format for devices that implement the WAP (Wireless Application Protocol) specification based on XML, such as mobile phones. ... The Extensible HyperText Markup Language, or XHTML, is a markup language that has the same depth of expression as HTML, but also conforms to XML syntax. ...

There are a number of ways to perform user agent sniffing within web applications, including using public domain scripts and even commercial products such as BrowserHawk. See the External Links section for details.

Some common user agent strings dissected

Internet Explorer, and browsers cloaking as Internet Explorer

 Mozilla/MozVer (compatible; MSIE IEVer[; Provider]; Platform[; Extension]*) [Addition] 


  • MozVer: Netscape compatibility version
    • 1.22: Internet Explorer 1.5 and 2.0
    • 2.0: Internet Explorer 3.x for Windows and Internet Explorer 2.1 for Mac
    • 3.0: Internet Explorer 3.x for Mac
    • 4.0: Internet Explorer 4.x and higher
  • IEVer: Internet Explorer version number, e.g.: 1.5, 3.01, 5.0b1, 6.0
  • Provider: Access provider, e.g.:
    • AOL Version
    • America Online Browser Version; revRevision: AOL Explorer (note, this breaks the rule of no semicolons in Provider values)
    • CS 2000
    • MSN Version
    • This parameter is included but empty on some Opera distributions, resulting in "semicolon space semicolon":
 ; ; 
  • Platform: Operating system, e.g.:
    • Windows 3.1 (including Windows NT 3.x)
    • Windows 95
    • Windows 98
    • Windows 98; Win 9x 4.90: Windows Millennium Edition (Windows Me)
    • Windows NT
    • Windows NT 4.0
    • Windows NT 5.0: Windows 2000
    • Windows 2000: Windows 2000 (used by Opera)
    • Windows NT 5.01: Windows 2000, Service Pack 1 (SP1)
    • Windows NT 5.1: Windows XP
    • Windows NT 5.2: Windows Server 2003
    • Windows NT 6.0: Windows Vista
    • Windows CE: Windows CE and Windows Mobile (used by Internet Explorer Mobile)
    • Win32: Seen with IE 7b1 on Windows XP
    • Mac_68000
    • Mac_PPC: Used up until IE 4.x
    • Mac_PowerPC: Used from IE 5.x and up
    • SunOS Version: SunOS
    • Symbian OS: Used by Opera on mobile phones
    • Nitro: Nintendo DS (used by Opera)
    • PSP: Playstation Portable
  • Extension: optional, a list of semicolon-separated extensions installed, e.g.:
    • .NET CLR Version: .NET Framework common language runtime installed (may appear multiple times, e.g. when both 1.1 and 2.0 are supported)
    • SV1: Internet Explorer 6 in Windows XP SP2 and Windows Server 2003 SP1 installed
    • Tablet PC Version: Tablet services are installed
    • Win64: 64-bit Windows
    • IA64: Intel Itanium processor
    • AMD64: x64 processor
    • x64: x64 processor
    • WOW64: 32-bit Internet Explorer is running on 64-bit Windows
    • Media Center PC Version: Windows MCE, where Version is:
      • 2.8: Media Center 2004
      • 3.0: Media Center 2005
      • 3.1: Media Center 2005 with update rollup 1
      • 4.0: Media Center 2005 with update rollup 2
      • 5.0: Windows Vista Home Premium or Ultimate edition.
    • MediaCenter Version: browsing from within Media Center interface
    • MSIECrawler: MSIE retrieving pages for Offline Content feature
    • X11: Internet Explorer on SunOS
    • PPC: Pocket PC (used by Internet Explorer Mobile)
    • Smartphone: Smartphone (used by Internet Explorer Mobile)
    • Motorola Type: Internet Explorer Mobile on Motorola mobile phone
    • Nokia Type/Version: Opera on Nokia mobile phone
    • Various 3rd party browser extensions, like: (R1 Version) (RealPlayer webbrowser), Alexa Toolbar, Maxthon, Crazy Browser Version, MyIE2, Avant Browser [avantbrowser.com], FDM
    • Language: some Opera versions seem to include the language code here (seen for Opera 8.5 on Windows XP)
    • WidthxHeight: some Internet Explorer Mobile browsers include the display resolution here
  • Addition
    • Netscape/Version: Netscape using MSHTML rendering engine
    • Opera Version [Language]: Opera cloaked as Internet Explorer

Example: Windows XP is a line of operating systems developed by Microsoft for use on general-purpose computer systems, including home and business desktops, notebook computers, and media centers. ... Windows Server 2003 is a server operating system produced by Microsoft. ...

 Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727) 

Internet Explorer 1.0

Internet Explorer 1.0 used an alternative user agent:

 Microsoft Internet Explorer/Version (Platform) 


  • Version: Windows version because IE was originally supposed to be included with Windows 95, e.g.: 4.0b1 for Internet Explorer 1.0 beta
  • Platform: operating system, e.g.: Windows 95


This only applies to earlier versions of Netscape. Netscape 6.0 or higher based on the Gecko engine should see the Mozilla section below

 Mozilla/Version[Gold] [[Language]][Provider] (Platform; Security[; SubPlatform][StandAlone]) 


  • Version: version number
  • Gold: includes HTML editor
  • Language: standardized two-letter language identifier, e.g.: en, 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 C-CCK-MCD (Client Customization Kit and Mission Control Desktop, for ISPs and OEMs)
  • Platform
    • Win16: Windows 3.x
    • Win95: Windows 95, where SubPlatform can be:
      • 16bit for 16-bit version of Netscape
    • Win98: Windows 98
    • WinNT: Windows NT 3.x
    • Windows NT 5.0: Windows 2000
    • Windows NT 5.1: Windows XP
    • X11, where SubPlatform is:
      • Distribution Version [Subversion], e.g.: Linux i586, SunOS 5.6 sun4u, IRIX 6.5 IP32
    • Macintosh, where SubPlatform is:
  • Security
    • U: strong security (USA)
    • I: weak security (International)
    • N: no security
  • StandAlone: standalone Navigator is indicated by ; Nav (X11 platforms), ;Nav (Windows, note missing space) or , Nav (on Macintosh), only for version 4.x

The Motorola 680x0/0x0/m68k/68k/68K family of CISC microprocessor CPU chips were 32-bit from the start, and were the primary competition for the Intel x86 family of chips in personal computers of the 1980s and early 1990s. ... PowerPC is a RISC microprocessor architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM. Originally intended for personal computers, PowerPC CPUs have since become popular embedded and high-performance processors as well. ... It has been suggested that x86 assembly language be merged into this article or section. ...


 Mozilla/MozVer (Platform; Security; SubPlatform; Language; rv:Revision[; Extension]*) Gecko/GeckVer [Product/ProdVer] 


  • MozVer: Netscape compatibility version
    • 5.0 for all known Mozilla browsers
  • Platform and SubPlatform
    • Windows
      • Win3.11: Windows 3.11
      • Win95: Windows 95
      • Win98: Windows 98
      • Win 9x 4.90: Windows Me
      • WinNT3.51: Windows NT 3.51
      • WinNT4.0: Windows NT 4.0
      • Windows NT 5.0: Windows 2000
      • Windows NT 5.1: Windows XP (except XP Professional x64 Edition)
      • Windows NT 5.2: Windows Server 2003 and Windows XP Professional x64 Edition
      • Windows NT 6.0: Windows Vista
      • Windows CE 4.21: Windows Mobile 2003
    • Macintosh
      • PPC Mac OS X
      • PPC Mac OS X Mach-O
      • Intel Mac OS X
    • X11
      • Linux [Version] Hardware
      • FreeBSD Hardware
      • NetBSD Hardware
      • OpenBSD Hardware
      • SunOS Hardware
  • Security
    • U: strong security (USA)
    • I: weak security (International)
    • N: no security
  • Language: standardized language identifier, e.g.: en, en-US, en-GB
  • Revision: e.g. m18, 1.0rc3, 1.7.8, 1.8a2
  • Extension
    • MultiZilla Version
  • GeckVer: Gecko (layout engine) compilation date, in the format YYYYMMDD
  • Product
    • For the Mozilla Application Suite, there is no Product or ProdVer. The Revision is the product version.
    • Netscape, Netscape6
    • Phoenix, Firebird, Firefox, GranParadiso (Firefox 3 codename), Minefield (trunk build)
    • K-Meleon
    • Minimo
    • SeaMonkey
    • Camino
    • CS 2000 7.0
  • ProdVer: Product version

PlayStation Portable

The PlayStation Portable has its own browser and User Agent:

 Mozilla/4.0 (PSP (PlayStation Portable); 2.00) 

The 2.00 means actually the firmware version, but Sony has never updated it. When the Internet browser published changed to firmware 2.00, it was not changed. A microcontroller, like this PIC18F8720 is controlled by firmware stored inside on FLASH memory In computing, firmware is a computer program that is embedded in a hardware device, for example a microcontroller. ...

PlayStation 3

the PlayStation 3 has its own browser and User Agent:

 Mozilla/5.0 (PLAYSTATION 3; SysVer) 
  • SysVer: The PS3 System Software Version


Opera/9.10 (Wii; U; ; 1621; en)

Opera/ProdVer (Wii; Security; ???; ???; Language)

Nintendo DS Browser

Mozilla/4.0 (compatible; MSIE 6.0; Nitro) Opera 8.5 The Nintendo DS Browser is a version of the Opera web browser for use on the Nintendo DS, developed by Opera Software and Nintendo. ...

Encryption strength "U" / "I" / "N"

Netscape, Mozilla, Opera and some others use one of these three letters to specify the browser's encryption strength. Since the US government formerly would not 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, supporting up to 256-bit encryption, since an international version is no longer required. Netscape Navigator, also known as Netscape, was a proprietary web browser that was popular during the 1990s. ... Mozilla was the official, public, original name of Mozilla Application Suite by the Mozilla Foundation, nowadays called SeaMonkey suite. ... Opera is an Internet suite which handles common internet-related tasks, including visiting web sites, sending and receiving e-mail messages, managing contacts, and online chat. ... “Encrypt” redirects here. ... Since World War II, Western governments, including the U.S. and its NATO allies have regulated the export of cryptography for national security considerations. ... Netscape Communications Corporation was the publisher of the Netscape Navigator web browser as well as many other internet and intranet client and server software products. ... The Mountain View office shared by the Mozilla Foundation and the Mozilla Corporation The Mozilla Foundation (abbreviated MF or MoFo) is a non-profit organization that exists to support and provide leadership for the open source Mozilla project. ...

See also

The robots exclusion standard or robots. ... A web crawler (also known as a Web spider or Web robot) is a program or automated script which browses the World Wide Web in a methodical, automated manner. ... WURFL stands for Wireless Universal Resource File. ... The User Agent Profile (UAProf) specification is concerned with capturing capability and preference information for wireless devices. ...

External links

Image File history File links Broom_icon. ...

Lists of user-agent strings in common use

  • User-agents.org, database of known user agent strings
  • Robots/crawlers DB From "ASAP Consulting".
  • Bots vs Browsers — user agent blog and extensive bot database
  • Browsers capabilities registry — A listing of many user agents along with supported capabilities

Tools for examining user-agent strings

  • User Agent Test User Agent Test Page
  • Online tool: What is My User-Agent? Includes code to detect user-agents in PHP, ASP, and JavaScript.
  • Automatically detect browsers and wireless devices (using BrowserHawk)
  • HPC:Factor Windows CE & Windows Mobile User Agents Listing & BrowsCap data
  • User agent string analysis
  • Display detailed analysis UA fragments with XML-RPC access

Other links



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