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".
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. 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. 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.
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). 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.
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. Never use the OS token to define if a browser is on mobile, tablet or desktop.
Microsoft Edge comes with a capability of changing user agent effortlessly. You can change the user agent of Microsoft Edge via Developer Tools menu.
As mentioned earlier above, changing user agent in Microsoft Edge is extremely easy. 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.
It allows sites to determine specific details, which in turn alters how the page is served to the user. For instance, menus will be easier to touch and read, and text will be more stripped down and readable.
Normally, users are oblivious to the exchange of browser user agent data; there are, however, ways in which users and developers can change the user agent to test for different platforms or simply to mask their browser ID. Browsers have a fingerprint that can help uniquely identify users with the user agent being one of these factors.
When using Edge, open a page and press the F12 key to access the developer settings. Select the “Emulation” tab and look for the Sergeant string list.” Here you can choose to make Edge mimic the browser of your choice.
Just as with Edge, Chrome has an user agent change within the developer settings, although it is a lot more complicated to access. From there click “Tools” and then “Developer Options.” You can also easily access this via the key combination of Ctrl + Shift + I.
Open a browser window and type about:config within the address bar. A warning will appear, but it is quite safe to proceed, providing you don’t change settings or flags without due care and attention.
If you don’t fancy the idea of messing with a browser’s settings, then there are some add-ons and extensions that will do the job for you. It is currently, at the time of writing this article, a featured extension from Firefox, so that may put to rest some concerns that users may have.
Matthew Muller Matt has worked in the tech industry for many years and is now a freelance writer. The new Microsoft Edge running on Chromium isn’t yet here officially, but a leaked build allows us to try out the browser in anticipation of its highly-anticipated release.
Using the browser on a daily basis isn’t obviously recommended as experimental builds like this can’t by any means become your main driver. For many users, switching to a different user agent and thus emulating another browser is a method to bypass certain website restrictions that concern a specific app.
For example, if a website doesn’t support Chromium, you can very well change the user agent to mimic a different browser like Mozilla Firefox. The best example is Skype for Web, which doesn’t work in Firefox anymore, so Mozilla users need to switch to another user agent to connect to the service.
For those unfamiliar with this screen, it’s specifically supposed to provide developers with advanced tools that let them analyze code and website performance. Changing the user agent is actually considered a developer option that helps webmasters check their pages against potential compatibility issues with different browsers.
By default, Microsoft Edge is configured to Select automatically the user agent, so you need to uncheck this option to be able to choose a custom setting. 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. The sergeant property has been aptly described as “an ever-growing pack of lies” by Patrick H. Lake in W3C discussions.
(“or rather, a balancing act of adding enough legacy keywords that won’t immediately have old UA-sniffing code falling over, while still trying to convey a little of actually useful and accurate information.”) 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. In our experience Microsoft Edge runs best on the ‘WebKit’ code paths in these sites.
They reveal a catalog of technical data about the device and software that the visitor is using. Armed with this information, you can develop richer and more dynamic websites that deliver different experiences based on the user agent that's visiting.
User agents are also critical in controlling search engine robots using the robots.txt file on your server. In order to leverage this information, you need to understand the component parts of an user agent string and consider also the potential risks of using this method to deliver content.
When the internet was a text-based system, right back at the beginning of its use, users had to type commands to navigate and send messages. We simply point and click, and the browser is acting as our agent,” turning our actions into commands.
This is a really set of data for web developers since it allows them to customize the experience depending on the user agent that's loaded the page. Browsers are a straightforward example of an user agent, but other tools can act as agents.
Plus a whole range of feed readers, validators, cloud platforms, media players, email libraries, and scripts. Once the user agent has identified itself to the web server, a process called content negotiation can begin.
The user agent application is Mozilla version 5.0, or a piece of software compatible with it. Note that a huge part of the user agent string is concerned with compatibility.
That's because Internet Explorer originally had to declare itself to be Mozilla compatible in order to receive content with frames. In practice, the majority of browsers now declare themselves to be Mozilla compatible to ensure that they can access all the content on the web.
More, we can feed that data back into a cycle of continuous improvement, analytics and other processes, like conversion optimization. As we mentioned in the introduction, search engine crawlers are a very specific type of user agent.
An user agent is a particular string of characters in each browser that allows acts as an identification agent. The user agent string contains the user application or software, the operating system (and their versions), the web client, the web client's version, and the engine responsible for the content display (such as Apple WebKit).
It is a rendering engine that processes HTML and CSS to interpret and present web pages. WebKit is also responsible for allowing you to navigate through links on a web page.
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. Some mobile web browsers will let you change what the browser identifies itself as (i.e. “Mobile Mode” or “Desktop Mode”) in order to access certain websites that only allow desktop computers.
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