What Does Your User Agent Say About You?


A user agent is a computer program representing a person, for example, a browser in a Web context.

Besides a browser, a user agent could be a bot scraping webpages, a download manager, or another app accessing the Web. Along with each request they make to the server, browsers include a self-identifying User-Agent HTTP header called a user agent (UA) string. This string often identifies the browser, its version number, and its host operating system.

Spam bots, download managers, and some browsers often send a fake UA string to announce themselves as a different client. This is known as user agent spoofing.

The user agent string can be accessed with JavaScript on the client side using the navigator.userAgent property.

A typical user agent string looks like this: "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:35.0) Gecko/20100101 Firefox/35.0".


User Agent String

Browser Data

User Agent Define

Danielle Fletcher
• Monday, 05 October, 2020
• 11 min read

During the first browser war, many web servers were configured to send web pages that required advanced features, including frames, to clients that were identified as some version of Mozilla only. Other browsers were considered to be older products such as Mosaic, Cello, or Samba, and would be sent a bare-bones HTML document.

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Automated agents are expected to follow rules in a special file called robots.txt “. 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 World Wide Web Consortium (W3C) or the Internet Engineering Task Force (IETF).

Websites often include code to detect browser version to adjust the page design sent according to the user agent string received. Thus, various browsers have a feature to cloak or spoof their identification to force certain server-side content.

For example, the Android browser identifies itself as Safari (among other things) in order to aid compatibility. User agent sniffing is the practice of websites showing different or adjusted content when viewed with certain user agents.

An example of this is Microsoft Exchange Server 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.

Web browsers created in the United States, such as Netscape Navigator and Internet Explorer, previously used the letters U, I, and N to specify the encryption strength in the user agent string. Until 1996, when the United States government disallowed encryption with keys longer than 40 bits to be exported, vendors shipped various browser versions with different encryption strengths.


^ a b RFC 3261, SIP: Session Initiation Protocol, IETF, The Internet Society (2002) ^ RFC 7231, Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content, IETF, The Internet Society (June 2014) ^ Net news Article Format. Browser Versions Carry 10.5 Bits of Identifying Information on Average “, Electronic Frontier Foundation, 27 January 2010.

I've been rejected until I come back with Netscape” ^ “Android Browser Reports Itself as Apple Safari”. ^ User Agent String explained: Android WebKit Browser”.

Mozilla/5.0 (Linux; U; Android 2.2; ends; HTC_DesireHD_A9191 Build/FRF91) Apple WebKit/533.1 (HTML, like Gecko) Version/4.0 Mobile Safari/533.1 ^ Emberton, Stephen. ^ “Chrome Phasing out Support for User Agent ".

UA's contain information such as the browser version, compatibility, operating system, and any modifying plugins. Using this data, a website can assess the capabilities of your computer, optimizing a page's performance and display.

Mozilla/4.0 is used for historical reasons as stated by Microsoft, not to be confused with the variants of Mozilla browsers, such as Firefox. Noted user agent string with Internet Explorer can have multiple .NET versions.


In the past, different encryption versions had to be released for specific parts of the world because of laws in the United States. Below is additional information about each of the different versions of Microsoft Windows and their corresponding user agent string codes.

For example, the button at the beginning of this page uses JavaScript to display your user agent string. However, if you want to gather the information or manipulate the data, it would be better to use a server-side scripting language, such as Perl.

The family of user agents also includes operating system shells, consumer electronics with Web-widgets, and stand-alone applications or embedded applications whose user interface is implemented as a combination of Web technologies. While rendering engines and other technologies used to build user agents are not by themselves considered user agents, it is fundamental to user agent accessibility that these technologies support user agent requirements.

In building an user agent the developer should fully understand the support for AAG 2.0 when selecting technologies. The following tests can be used to determine if software qualifies as an user agent for the purposes of these guidelines.

User agent refers to the application that remotely accesses a different computer, usually a server, through the network. It means that the Web browser you're using is accessing a program (such as Gmail) or a service (such as that operates on some other faraway computer.

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Your computer (the client) is connecting to the desired Web page (the server) through one of the TCP/IP protocols. When you key in a “query” on your Web browser (user agent) and hit “enter,” a text string (a programming sequence of symbols) is sent to the server of that website.

While the text string identifies itself to the server as an user agent, it simultaneously requests access to the website. When the Internet was young, the World Wide Web was dominated by a few of the first generation of browsers.

As a result, many Web servers were designed to interact and connect with only those leading browsers. This was possible because the website could identify that Web browser as the user agent by its text string when it requested access to the site.

To overcome this roadblock, competing browsers were modified to replicate or impersonate text strings that would be accepted by the website. An early example of this is when the browser Internet Explorer spoofed its primary rival at the time, Netscape Navigator.

The Chrome (or Chromium/Blink-based engines) user agent string is similar to Firefox’s. For compatibility, it adds strings like HTML, like Gecko and Safari.

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The Opera browser is also based on the Blink engine, which is why it almost looks the same, but adds “Or/”. In this example, the user agent string is mobile Safari’s version.

The user agent string identifies the browser as IE 9 with the Trident 5 rendering engine. The plot thickens: Chrome is pretending to be both Mozilla and Safari.

Eventually, Microsoft’s Internet Explorer came along and it supported frames, too. In this way, browser developers kept adding words to their user agents over time.

He's written about technology for nearly a decade and was a World columnist for two years. Chris has written for The New York Times, been interviewed as a technology expert on TV stations like Miami's NBC 6, and had his work covered by news outlets like the BBC.

Since 2011, Chris has written over 2,000 articles that have been read more than 500 million times---and that's just here at How-To Geek. There's no “standard” way of writing an user agent string, so different web browsers use different formats (some are wildly different), and many web browsers cram loads of information into their user agents.

user customized agent enter example

Regarding the concept user agent style sheet”, consult section Cascade in the CSS 2.1 spec. They are just the rock bottom: in the absence of any style sheets provided by the page or by the user, the browser still has to render the content somehow, and the user agent style sheet just describes this.

Marking the document as HTML5 by the proper doc type on the first line, solved my issue. In order to present the page in a way that satisfies ” general presentation expectations.” For example, a default style sheet would provide base styles for things like font size, borders, and spacing between elements.

It is common to employ a reset style sheet to deal with inconsistencies amongst browsers. An useragent's default style sheet should present the elements of the document language in ways that satisfy general presentation expectations for the document language.

Peter Mortensen 27.2k2121 gold badges9393 silver badges123123 bronze badges Define the values that you don't want to be used from Chrome's user agent style in your own CSS content.

Peter Mortensen 27.2k2121 gold badges9393 silver badges123123 bronze badges So the right way to beat this: If you type the command line directly in the .html source code, this beats the .css file, in that way, you told the browser directly what to do and the browser is at position not to read the commands from the .css file.

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I had a dumb error where a button element didn't look right in Chrome. So Chrome was stepping in to supply the parts that it thought I was missing.

I'm working on a web page in Google Chrome. In Chrome developer tools, it says user agent stylesheet in place of the CSS file name.

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