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.
A typical user agent string looks like this: "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:35.0) Gecko/20100101 Firefox/35.0".
You can change it via Developer Tools menu which you can access by clicking the three-dot icon in the top-right corner of Microsoft Edge. An user agent (UA) string is able to be used to detect what version of a specific browser is being used on a certain operating system.
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. In these cases, Microsoft uses a list of UA overrides in our Beta and Stable channels to maximize compatibility for users who access these sites.
You’ll also notice that the entire string ends with Edge /12.0, which Chrome does not. There are ways to develop your website to progressively enhance itself based on the availability of features rather than by targeting specific browsers.
Often, lazy developers will just sniff for the UA string and disable content on their website based on which browser they believe the viewer is using. Internet Explorer 8 is a common point of frustration for developers, so they will frequently check if a user is using ANY version of IE, and disable features.
For example, the Modernize library is a fantastic and simple way of detecting features. Over the past year, we’ve seen some UA-sniffing sites that have been updated to detect Microsoft Edge … only to provide it with a legacy IE11 code path.
While all phones come with pre-installed browsers, both Google Play and Apple App Store offer a number of alternative browsers, some focusing on speed and lightness, others on saving bandwidth and blocking ads, and an ever-increasing amount claiming to increase privacy and reduce a users' mobile digital footprint. Feel free to browse the stats for your local market using our Data Explorer tool.
Optimize UX and conversion rate on mobile Boost web performance Target ads and analyze web traffic Enable App analytics and advertising insights The Microsoft Edge DevTools provide a collection of features to help you emulate mobile devices.
Instead, you simulate the mobile user experience from your laptop or desktop. When in doubt, your best bet is to actually run your page on a mobile device.
You may view, change, debug, profile, or all four while you interact with the code. Choose Toggle device emulation () or choose To customize and control DevTools (...) > Device emulation to open the UI that enables you to simulate a mobile viewport.
By default, the Device Toolbar opens in Responsive Viewport Mode. To quickly test the look and feel of your page across multiple screen sizes, drag the handles to resize the viewport to your required dimensions.
Choose a breakpoint to change the width of the viewport so that the media query gets triggered. The following table describes the differences between the available device type options.
OptionRendering methodCursor convents triggered Mobile Mobile Circle touch Mobile (no touch) Mobile NormalclickDesktopDesktopNormalclickDesktop (touch)DesktopCircletouchIf the Device Type list is not displayed, choose More options > Add device type. The Rotate button disappears if your Device Toolbar is narrow.
Mobile devices often have network and CPU constraints. Ensure you test how quickly your page loads and how it responds at different internet and CPU speeds.
Mid-tier mobile simulates fast 3G and throttles your CPU. All the throttling is based upon the normal capability of your laptop or desktop.
If the Throttle list is hidden, your Device Toolbar is too narrow. To access the Throttle list, increase the width of the Device Toolbar.
To throttle the CPU only and not the network, complete the following steps. Or select Control + Shift + P (Windows, Linux) or Command + Shift + P (macOS) to open the Command Menu, type 3G, and choose To enable fast 3G throttling or Enable slow 3G throttling.
Choose To customize and control DevTools (...) > More tools > Sensors. Choose To customize and control DevTools (...) > More tools > Sensors.
If your page depends on the user agent string from a mobile device to render properly, use the Network conditions panel to provide different user agent strings. Choose To customize and control DevTools (...) > More tools > Network conditions.
Then, choose Custom... to select from a list of predefined user agent strings. Use the following options to discuss the new features and changes in the post, or anything else related to DevTools.
Send your feedback using the Send Feedback icon or select Alt + Shift + I (Windows, Linux) or Option + Shift + I (macOS) in DevTools. To file bugs about this article, use the following Feedback section.
The Send Feedback icon in Microsoft Edge DevTools 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. The difficulty of successfully using user agent detection is worth a few disruptions to the purity of your HTML.
Also, rethink your design: can you use progressive enhancement or fluid layouts to help remove the need to do this? 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. People use user agent sniffing to detect if the users' device is touch-friendly and has a small screen, so they can optimize their website accordingly.
While user agent sniffing can sometimes detect these, not all devices are the same: some mobile devices have big screened sizes, some desktops have a small touchscreen, some people use smart TV's which are an entirely different ballgame altogether, and some people can dynamically change the width and height of their screen by flipping their tablet on its side! 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. 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.
One such case is using user agent sniffing as a fallback when detecting if the device has a touch screen. Internet Explorer (on Windows) and WebKit (on iOS) are two perfect examples.
However, Internet Explorer was such a special little wasp exception prior to version 9 that it was very easy to detect the browser based upon the browser-specific features available. 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.
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 StringEdgeHTML Edge /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.