271:: This is used by the browser to indicate specific enhancements that are available directly in the browser or through third parties. An example of this is Microsoft Live Meeting which registers an extension so that the Live Meeting service knows if the software is already installed, which means it can provide a streamlined experience to joining meetings.
349:(IETF). Websites often include code to detect browser version to adjust the page design sent according to the user agent string received. This may 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 have a feature to
144:, where the origin server selects suitable content or operating parameters for the response. For example, the user agent string might be used by a web server to choose variants based on the known capabilities of a particular version of client software. The concept of content tailoring is built into the HTTP standard in
400:
2003's
Outlook Web Access feature. When viewed with Internet Explorer 6 or newer, more functionality is displayed compared to the same page in any other browsers. User agent sniffing is considered poor practice, since it encourages browser-specific design and penalizes new browsers with unrecognized
283:
was the most widely used web browser that did not have the user agent string with "Mozilla" (instead beginning it with "Opera"). Since July 15, 2013, Opera's user agent string begins with "Mozilla/5.0" and, to avoid encountering legacy server rules, no longer includes the word "Opera" (instead using
323:
strength in the user agent string. Until 1996, when the United States government allowed encryption with keys longer than 40 bits to be exported, vendors shipped various browser versions with different encryption strengths. "U" stands for "USA" (for the version with 128-bit encryption), "I" stands
340:
The popularity of various Web browser products has varied throughout the Web's history, and this has influenced the design of websites in such a way that websites are sometimes designed to work well only with particular browsers, rather than according to uniform standards by the
93:. The user agent for the operator of a computer used to access the Web has encoded within the rules that govern its behavior the knowledge of how to negotiate its half of a request-response transaction; the user agent thus plays the role of the
401:
user agent identifications. Instead, the W3C recommends creating standard HTML markup, allowing correct rendering in as many browsers as possible, and to test for specific browser features rather than particular browser versions or brands.
101:. Often considered useful in networks is the ability to identify and distinguish the software facilitating a network session. For this reason, the User-Agent HTTP header exists to identify the client software to the responding server.
457:
announced it would temporarily freeze portions of the browser's user agent string at version 109. This was done due to several websites incorrectly recognizing a development version of the browser (which identified itself by the string
162:
As with many other HTTP request headers, the information in the user agent string contributes to the information that the client sends to the server, since the string can vary considerably from user to user.
292:
Automated web crawling tools can use a simplified form, where an important field is contact information in case of problems. By convention the word "bot" is included in the name of the agent. For example:
175:. The format of the user agent string in HTTP is a list of product tokens (keywords) with optional comments. For example, if a user's product were called WikiBrowser, their user agent string might be
709:
481:). The problem will self-correct after the release of Firefox 120, as only browsers identifying themselves as 110 through 119 were observed to be affected by it.
787:
735:
752:
Mozilla/5.0 (Linux; U; Android 2.2; en-sa; HTC_DesireHD_A9191 Build/FRF91) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1
329:
324:
for "International" – the browser has 40-bit encryption and can be used anywhere in the world – and "N" stands (
1008:
151:
The user agent string is one of the criteria by which Web crawlers may be excluded from accessing certain parts of a website using the
89:
comprises the name of the header itself, the header value that a given user agent uses to identify itself is colloquially known as its
396:
is the practice of websites showing different or adjusted content when viewed with certain user agents. An example of this is
713:
655:
434:. They stated that other major web browser vendors were supportive of the move. Google stated that a new feature called
441:
Starting with Chrome 113, released in April 2023, User-Agent header stays the same except for the major version part.
847:
586:
357:
their identification to force certain server-side content. For example, the
Android browser identifies itself as
346:
237:
Mozilla/5.0 (iPad; U; CPU OS 3_2_1 like Mac OS X; en-us) AppleWebKit/531.21.10 (KHTML, like Gecko) Mobile/7B405
801:
622:
117:
to its operating peer. In HTTP, SIP, and NNTP protocols, this identification is transmitted in a header field
1003:
973:"Remove the frozen 'rv:109.0' IE11 UA workaround after Firefox reaches version 120 (desktop and Android)"
739:
376:
42:
109:
When a software agent operates in a network protocol, it often identifies itself, its application type,
495:
431:
17:
510:
500:
397:
342:
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114:
113:, device model, software vendor, or software revision, by submitting a characteristic identification
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browser as it's no longer required for determining browser capabilities and instead mainly used for
792:
206:
126:
98:
822:
677:
205:, many web servers were configured to send web pages that required advanced features, including
947:"Freeze 'rv:' segment in the User Agent string to 'rv:109.0' to avoid erroneous IE11 detection"
618:
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276:
172:
895:
600:
470:
358:
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8:
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218:
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Websites intended for display by mobile phones often rely on user agent sniffing, since
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316:
642:
590:
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698:
Burstein complaining "... I've been rejected until I come back with
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148:"for the sake of tailoring responses to avoid particular user agent limitations".
871:
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603:
405:
130:
545:
426:
announced that they would be freezing parts of the User-Agent header in their
247:: Previously used to indicate compatibility with the Mozilla rendering engine.
145:
997:
427:
228:
For this reason, most Web browsers use a user agent string value as follows:
85:
responsible for making a given HTTP request. Whereas the character sequence
435:
202:
122:
520:
467:
171:
The user agent string format is currently specified by section 10.1.5 of
619:"Browser Versions Carry 10.5 Bits of Identifying Information on Average"
299:
Automated agents are expected to follow rules in a special file called "
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320:
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only. Other browsers were considered to be older products such as
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would replace the functionality of the user agent string.
372:, often have the ability to change the user agent string.
179:. The "most important" product component is listed first.
319:, previously used the letters U, I, and N to specify the
166:
253:: Details of the system in which the browser is running.
234:
For example, Safari on the iPad has used the following:
328:) for "None" (no encryption). Following the lifting of
375:
A result of user agent spoofing may be that collected
921:"www.bestbuy.com - Firefox is an unsupported browser"
736:"User Agent String explained: Android Webkit Browser"
287:
209:, to clients that were identified as some version of
361:(among other things) in order to aid compatibility.
411:
311:Web browsers created in the United States, such as
140:In HTTP, the "user agent string" is often used for
848:"Google to phase out user-agent strings in Chrome"
995:
710:"Android Browser Reports Itself as Apple Safari"
306:
296:Googlebot/2.1 (+http://www.google.com/bot.html)
225:, and would be sent a bare bones HTML document.
656:"Opera User Agent Strings: Opera 15 and Beyond"
284:the string "OPR" to denote the Opera version).
240:The components of this string are as follows:
788:"Browser Detection and Cross Browser Support"
332:, most vendors supported 256-bit encryption.
125:, such as Web crawlers, often also include a
444:
251:(iPad; U; CPU OS 3_2_1 like Mac OS X; en-us)
823:"Chrome Phasing out Support for User Agent"
669:
475:Mozilla/5.0 (Windows NT 10.0; Trident/7.0;
23:
757:
24:
616:
594:
182:The parts of this string are as follows:
104:
59:Not to be confused with the concept of a
675:
643:History of the browser user-agent string
526:Wireless Universal Resource File (WURFL)
32:This is an accepted version of this page
14:
996:
560:
538:
408:often differ greatly from each other.
382:
335:
167:Format for human-operated web browsers
785:
763:
738:. UserAgentString.com. Archived from
460:Mozilla/5.0 (Windows NT 10.0; Win64;
137:can contact the operator of the bot.
970:
944:
617:Eckersley, Peter (27 January 2010).
1009:Hypertext Transfer Protocol headers
845:
589:. November 2009. sec. 3.2.13.
570:, IETF, The Internet Society (2002)
66:Software acting on behalf of a user
56:
288:Format for automated agents (bots)
57:
1020:
676:Zawinski, Jamie (28 March 1998).
364:Other HTTP client programs, like
568:SIP: Session Initiation Protocol
412:Deprecation of User-Agent header
259:: The platform the browser uses.
81:header intended to identify the
964:
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786:Clary, Bob (10 February 2003).
779:
766:"W3C Markup Validation Service"
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678:"user-agent strings (obsolete)"
453:110 released in February 2023,
377:statistics of Web browser usage
347:Internet Engineering Task Force
702:
691:
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623:Electronic Frontier Foundation
610:
573:
464:) Gecko/20100101 Firefox/110.0
13:
1:
658:. dev.opera.com. 15 July 2013
531:
307:Encryption strength notations
7:
506:User Agent Profile (UAProf)
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265:: Browser platform details.
193:layout engine and version (
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1025:
546:"RFC-9110: HTTP Semantics"
496:List of HTTP header fields
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386:
186:product name and version (
58:
501:Robots exclusion standard
445:Browser misidentification
398:Microsoft Exchange Server
343:World Wide Web Consortium
177:WikiBrowser/1.0 Gecko/1.0
153:Robots Exclusion Standard
793:Mozilla Developer Center
275:Before migrating to the
39:latest accepted revision
896:"Firefox Release Notes"
872:"User-Agent Reduction"
582:Netnews Article Format
432:browser fingerprinting
105:Use in client requests
257:AppleWebKit/531.21.10
977:bugzilla.mozilla.org
951:bugzilla.mozilla.org
764:Pemberton, Stephen.
511:User-Agent Reduction
471:Internet Explorer 11
99:client–server system
1004:Clients (computing)
394:User agent sniffing
383:User agent sniffing
336:User agent spoofing
330:export restrictions
263:(KHTML, like Gecko)
142:content negotiation
29:Page version status
945:Schubert, Dennis.
846:Cimpanu, Catalin.
516:Web browser engine
313:Netscape Navigator
35:
971:Peterson, Chris.
716:on August 6, 2011
418:HTTP Client Hints
366:download managers
317:Internet Explorer
201:During the first
91:user agent string
75:User-Agent header
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491:Browser sniffing
480:
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379:are inaccurate.
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231:Mozilla/ () ()
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279:code base,
245:Mozilla/5.0
203:browser war
998:Categories
925:github.com
881:2023-07-13
857:2020-03-25
832:2020-03-25
808:2009-05-30
772:2011-10-18
684:2010-01-08
662:2014-05-05
566:RFC 3261,
532:References
468:deprecated
321:encryption
301:robots.txt
157:robots.txt
119:User-Agent
87:User-Agent
83:user agent
61:user agent
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720:August 9,
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628:25 August
466:) as the
422:In 2020,
195:Gecko/1.0
135:Webmaster
71:computing
485:See also
462:rv:110.0
326:de facto
277:Chromium
146:RFC 1945
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982:8 April
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930:8 April
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552:28 July
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428:Chrome
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