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".
For compatibility, it adds strings like HTML, like Gecko and Safari. The Opera browser is also based on the Blink engine, which is why it almost looks the same, but adds “Or/
Spam bots, download managers, and some browsers often send a fake UA string to announce themselves as a different client. The specification asks browsers to provide as little information via this field as possible.
Opera 6+ allows users to set the browser identification string via a menu. A Hamstring specifying the complete user agent string the browser provides both in HTTP headers and in response to this and other related methods on the Navigator object.
The user agent string is built on a formal structure which can be decomposed into several pieces of info. 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.
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.
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.
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. 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 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.
If the device is large enough that it's not marked with “Mob”, you should serve your desktop site (which, as a best practice, should support touch input anyway, as more desktop machines are appearing with touchscreens). Firefox OS phones say Mobile “; the web is the platform.
Appname / app version indicates the application name and version. Firefoxversion will generally represent the equivalent Firefox release corresponding to the given Gecko version.
When Firefox runs on a device that has the phone form factor, there is a Mobile; token in the platform part of the UA string. The preferred way to target content to a device form factor is to use CSS Media Queries.
This way, your code will work if/when Firefox ships on other phone/tablet operating systems or Android is used for laptops. Firefox OS devices identify themselves without any operating system indication; for example: “Mozilla/5.0 (Mobile; RV:15.0) Gecko/15.0 Firefox/15.0”.
Some of them we have noticed are of the form Nelson; “, Reopen; “, or Open C; (note that putting space is also discouraged). Firefox OS version numberGecko version number1.0.118.01.118.11.226.01.328.01.430.02.032.02.134.02.2372.544It's easy to find the correspondences by looking at the Mercurial repository names : repositories starting by mozilla-b2g are the release repositories for Firefox OS, and have both Firefox OS and Gecko versions in their names.
The first two digits are owned by the Mozilla product team and denote versions with new features (e.g.: v1.1, 1.2, etc). The third digit is incremented with regular version tags (about every 6 weeks) for security updates, and the fourth is owned by the OEM.
BrowserGecko user agent string Firefox for Memo (Nokia N900)Mozilla/5.0 (Memo; Linux armv7l; RV:10.0.1) Gecko/20100101 Firefox/10.0.1 Fennec/10.0.1Camino on Mac Mozilla/5.0 (Macintosh; Intel Mac OS X 10.5; RV:2.0.1) Gecko/20100101 Firefox/4.0.1 Camino/2.2.1SeaMonkey on Windows Mozilla/5.0 (Windows NT 5.2; RV:10.0.1) Gecko/20100101 Firefox/10.0.1 Monkey/2.7.1SeaMonkey on Mac Mozilla/5.0 (Macintosh; Intel Mac OS X 10.5; RV:10.0.1) Gecko/20100101 Firefox/10.0.1 Monkey/2.7.1SeaMonkey on Linux Mozilla/5.0 (X11; Linux i686; RV:10.0.1) Gecko/20100101 Firefox/10.0.1 Monkey/2.7.1Prior to Firefox 4 and Gecko 2.0, it was possible for extensions to add user agent parts through the general.user agent.extra. Identifier preferences, (see the obsolete Sergeant Strings Reference).
In the past, specific plug-ins, add-ons or extensions added user agent parts to notify sites they were installed. The recommended way to do this, if it's absolutely necessary (remember that it slows down every request) is to set a custom HTTP header.
The cascade is an algorithm that defines how to combine property values originating from different sources. It lies at the core of CSS, as emphasized by the name: Cascading Style Sheets.
Though style sheets come from these different origins, they overlap in scope; to make this work, the cascade algorithm defines how they interact. Some browsers use actual style sheets for this purpose, while others simulate them in code, but the end result is the same.
The cascading algorithm determines how to find the value to apply for each property for each document element. That means rules whose selector matches the given element and which are part of an appropriate media at-rule.
A very simple introduction to the CSS cascade CSS Key Concepts: CSS syntax, at-rule, comments, specificity and inheritance, the box, layout modes and visual formatting models, and margin collapsing, or the initial, computed, resolved, specified, used, and actual values. Definitions of value syntax, shorthand properties and replaced elements.
Its syntax was defined as the software product name, with an optional slash and version designated “. The prose already invited people to use it for analytics and identify the products with implementation issues.
Updating databases and algorithms for identifying correctly is a very high maintenance task which is doomed to fail at a point in the future. New solutions are being developed for helping people to adjust the user experience depending on the capabilities of the products, not its name.
Responsive design helps to create Websites that are adjusting for different screen sizes. You could fall in the same traps as the ones existing with user agent detection algorithms.
User agent detection leads to situation where a new player can hardly enter the market even if it has the right set of technologies. Remember that there are huge benefits to create a system which is resilient to many situations.
We recommend you to limit your detection to the simplest possible string by matching the substring mob in lowercase. Remember that whatever the number of tokens you put there, you will fail at a point in the future.
There will be many road blocks on the way depending on the context, the business requirements, the social infrastructure of your own company. He regularly also blogs at http://robertnyman.com and loves to travel and meet people.
On Desktop, gecko trail is the fixed string “20100101” Firefox/firefoxversion indicates the browser is Firefox, and provides the version (such as 17.0”). The Chrome (or Chromium/blink-based engines) user agent string is similar to the Firefox format.
For compatibility, it adds strings like “HTML, like Gecko” and “Safari”. The Opera browser is also based on the blink engine, which is why it almost looks the same, but adds “Or/
My JS code has thousands of navigator checks You've basically just discovered the ultimate reason why doing UA string detection is considered awful practice.
Even without browser vendors deliberately changing their UA strings to break this kind of code (which they do), your task is fundamentally never-ending; you're going to have to keep revisiting this code every time a new device/browser/version is released, and your thousands of lines of code just will keep getting bigger and bigger. Plus of course, it will be completely unreliable if a user modifies his browser's UA string.
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.