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

Map User Agent To Web Browser

David Lawrence
• Saturday, 31 July, 2021
• 12 min read

Whenever you browse the internet, any server is able to identify your web browser and the host OS of your system. It encodes the browser version, operating system and other small features to the server.

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It’s not a big deal, it’s just a small trick that can do wonders in many cases. Google Chrome is one of the most powerful web browsers for all platforms.

I’d love to fool servers with Linux host despite running on Windows. Opera is a Chrome-based browser, sharing a lot of similarities in the core.

There are ways to develop your website to progressively enhance itself based on the availability of features rather than by targeting specific browsers. Using the user agent to detect the browser looks simple, but doing it well is, in fact, a very hard problem.

Also, experts, or people with another point of view, can give you ideas for working around the bug. If the problem seems uncommon, it's worth checking if this bug has been reported to the browser vendor via their bug tracking system (Mozilla ; WebKit ; Blink ; Opera).

Your site needs to use a specific Web feature that some browsers don't yet support, and you want to send those users to an older Website with fewer features but that you know will work. This is the worst reason to use user agent detection because odds are eventually all the other browsers will catch up.

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In those rare cases where behavior differs between browsers, instead of checking the user agent string, you should instead implement a test to detect how the browser implements the API and determine how to use it from that. Support could have been added to other browsers at any time, but this code would have continued choosing the inferior path.

As the above code demonstrates, there is always a way to test browser support without user agent sniffing. For example, in the above code snippets, using look behind in short-regexp notation (e.g. /reg/IGM) will cause a parser error in unsupported browsers.

Progressive enhancement This design technique involves developing your Website in 'layers', using a bottom-up approach, starting with a simpler layer and improving the capabilities of the site in successive layers, each using more features. Graceful degradation This is a top-down approach in which you build the best possible site using all the features you want, then tweak it to make it work on older browsers.

Rather, add in touch conveniences such as bigger, more easily clickable buttons (you can do this using CSS by increasing the font size). Here is an example of code that increases the padding of #exampleButton to 1em on mobile devices.

This effect can be easily achieved using CSS flex boxes, sometimes with floats as a partial fallback. Also try to move less relevant/important information down to the bottom and group the page's content together meaningfully. Although it is off-topic, perhaps the following detailed example might give you insights and ideas that persuade you to forgo user agent sniffing.

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The boxes can be separated into multiple columns via two equally fair method. The second method uses a Column layout and resents all the dogs to the left and all the cats to the right.

Only in this particular scenario, it is appropriate to provide no fallback for the flex boxes/multi columns, resulting in a single column of very wide boxes on old browsers. If more people visit the webpage to see the cats, then it might be a good idea to put all the cats higher in the source code than the dogs so that more people can find what they are looking for faster on smaller screens where the content collapses down to one column. Next, always make your code dynamic.

The user can flip their mobile device on its side, changing the width and height of the page. Or, there might be some weird flip-phone-like device thing in the future where flipping it out extends the screen.

The simplest way to do this is to separate all the code that moves content around based on screen size to a single function that is called when the page is loaded and at each resize event thereafter. Also note that there is a huge difference between the media queries (max-width: 25em), not all and (min-width: 25em), and (max-width: 24.99em) : (max-width: 25em) excludes (max-width: 25em), whereas not all and (min-width: 25em) includes (max-width: 25em).

Always be very deliberate about choosing the right media query and choosing the right >=, , >, or < in any corresponding JavaScript because it is very easy to get these mixed up, resulting on the website looking working right at the screen size where the layout changes. One such case is using user agent sniffing as a fallback when detecting if the device has a touch screen.

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Internet Explorer (on Windows) and WebKit (on iOS) are two perfect examples. WebKit is a bit worse because Apple forces all the browsers on IOS to use WebKit internally, thus the user has no way to get a better more updated browser on older devices.

For example, WebKit 6 has a bug whereby when the device orientation changes, the browser might not fire MediaQueryList listeners when it should. Most browsers set the name and version in the format BrowserName/VersionNumber, with the notable exception of Internet Explorer.

So to detect Safari you have to check for the Safari string and the absence of the Chrome string, Chromium often reports itself as Chrome too or Sea monkey sometimes reports itself as Firefox. Also, pay attention not to use a simple regular expression on the BrowserName, user agents also contain strings outside the Keyword/Value syntax.

Must containment not containFirefoxFirefox/xyzSeamonkey/xyzSeamonkeySeamonkey/xyzChromeChrome/chromium/xyzChromiumChromium/xyzSafariSafari/chrome/XYZ or Chromium/safari gives two version numbers: one technical in the Safari/XYZ token, and one user -friendly in a Version/XYZ tokenizer Opera 15+ (Blink-based engine) The browser version is often, but not always, put in the value part of the BrowserName/VersionNumber token in the Sergeant String.

There are five major rendering engines: Trident, Gecko, Presto, Blink, and WebKit. It is therefore important to pay attention not to trigger false-positives when detecting the rendering engine.

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Must containGeckoGecko/xyzWebKitAppleWebKit/pay attention, WebKit browsers add a 'like Gecko' string that may trigger false positive for Gecko if the detection is not careful. PrestoOpera/XYZ Note: Presto is no longer used in Opera browser builds >= version 15 (see 'Blink')Trident Trident/Internet Explorer put this token in the comment part of the Sergeant StringEdgeHTMLEdge/the non-Chromium Edge puts its engine version after the Edge/ token, not the application version. Note: Edge HTML is no longer used in Edge browser builds >= version 79 (see 'Blink'). BlinkChrome/XYZ Most rendering engines put the version number in the RenderingEngine/VersionNumber token, with the notable exception of Gecko.

The Operating System is given in most Sergeant strings (although not web -focused platforms like Firefox OS), but the format varies a lot. They indicate the OS, but also often its version and information on the relying on hardware (32 or 64 bits, or Intel/PPC for Mac).

Like in all cases, these strings may change in the future, one should use them only in conjunction with the detection of already released browsers. A technological survey must be in place to adapt the script when new browser versions are coming out.

The most common reason to perform user agent sniffing is to determine which type of device the browser runs on. Never assume that a browser or a rendering engine only runs on one type of device.

Never use the OS token to define if a browser is on mobile, tablet or desktop. Internet Explorer Immobile/XYZ token in the comment. Mozilla/5.0 (compatible; MSI 9.0; Windows Phone OS 7.5; Trident/5.0; Immobile/9.0)Edge on Windows 10 Mobile/XYZ & Edge/ tokens outside the comment. Mozilla/5.0 (Windows Phone 10.0; Android 6.0.1; Xbox; Xbox One) Apple WebKit/537.36 (HTML, like Gecko) Chrome/58.0.3029.110 Mobile Safari/537.36 Edge/16.16299In summary, we recommend looking for the string “Mob” anywhere in the Sergeant to detect a mobile device.

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User agent is a string used by web servers to identify a web browser they are connected to. Web servers need to identify every web browser they are connected to be able to know how they should serve the associated browser.

For instance, if a web server identifies a browser as Firefox running on Android, it will serve web pages specialized for mobile device instead of desktop. But, in case you are curious about the user agent of the web browser you are using, there are several resources you can take advantage of.

Simply visit this page to view the user agent of your web browser. For instance, if you are using Google Chrome running on Windows 10, you can change the user agent to Firefox on iPhone so the web servers will serve the web pages specialized for mobile device, iPhone in this case.

Platform identifiers change based on the operating system being used, and version numbers also increment as time passes. Mapping UA string tokens to a more human-readable browser name for use in code is a common pattern on the web today.

When mapping the new Edge token to a browser name, Microsoft recommends using a different name than the one developer used for the legacy version of Microsoft Edge to avoid accidentally applying any legacy workarounds that are not applicable to Chromium-based browsers. When Microsoft is notified about these types of issues, website owners are contacted and informed about the updated UA.

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This feature is useful for SEO professionals, for example, to identify issues with cloaking which is against Google’s Webmaster Guidelines or auditing websites which has different look depending on the device. User agent is an HTTP request header string identifying browser, application, operating system which connects to the server.

Verbose : Could be one of “true” or “false” values which indicates whether the page uses all methods or just the active one. Browsers are the basic internet need which require loads of security policies, server agreements, and connectivity codes to run ideally.

User agents are present in HTTP headers when the browser wants to communicate with a server. Each browser has its specific user agent string and web servers utilize this information to deliver appropriate material across different operating systems.

An example of this is the mobile version of webpages in devices; usually slimmed down and organized vertically for user ease. Web servers provide the bots with special treatments and verifications such as mandatory registrations, screens, etc.

Mozilla was considerably more advanced in terms of connectivity and security than Mosaic because of the ease of supported frames it provided. This was a remarkable advancement considering the other browsers made use of sending old pages without any frames at all.


However, there was still no receiving end of webpages with frames, because they were just shared with Mozilla browsers. 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.

Practically every time you access a high-traffic website, its server will be taking into account what your current user agent is, which helps identify your operating system and browser, in an attempt to better deliver content to you. Even popular browsers such as Chrome, Firefox, and Safari can often display web content in inconsistent ways when compared with each other.

But there are hundreds of user agents out there, ranging from browsers you’ve probably never heard of to email and RSS readers. In this article, we’ll discuss the technical side of user agents and how you can take advantage of software and browser plugins to manipulate how content is shown on the web.

Though it’s not nearly as common as it was a decade ago, you’ll sometimes see websites that claim incompatibility with a certain browser build and will completely deny access to anyone using it. While an user agent won’t identify you anywhere near as narrowly as an IP address, you’re still giving up the way you browse.

Nowadays, most popular browsers include a developer console that will allow you to change all sorts of things, such as your viewing resolution and user agent. The problem is that if you intend to change your user agent frequently, going through the steps to take it through a developer console can be tedious.

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This Chrome extension has nearly two million total users and was developed by Google, so its compatibility with the browser should be as good as you’ll ever find. Once installed, this extension adds a button to the right of the address bar that allows you to select through a total of eight browsers and mobile operating systems.

Other Articles You Might Be Interested In

01: Php Check User Agent
02: Php Get User Agent String
03: Php User Agent Parser
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