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What Does Your User Agent Say About You?

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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".

(Source: Mozilla.org)

User Agent String

Browser Data

User Agent Regex

author
James Lee
• Friday, 23 October, 2020
• 15 min read

Making statements based on opinion; back them up with references or personal experience. There are ways to develop your website to progressively enhance itself based on the availability of features rather than by targeting specific browsers.

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(Source: www.screamingfrog.co.uk)

Contents

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.

regex field agent agenty 1096 kb
(Source: www.agenty.com)

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.

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(Source: community.broadcom.com)

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.

regex lsp discussion
(Source: www.tvaddons.co)

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.

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(Source: www.youtube.com)

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). Making statements based on opinion; back them up with references or personal experience.

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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(Source: support.citrix.com)

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. I'm not super sure which section (if any) this belongs in, but I was wondering if anyone had advice for matching based on regex strings.

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.

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.

Mobile Safari).*(Or)/(\d+)\.(\d+)\. (\d+)'family_replacement: 'Opera Mobile'# Opera 15 for Desktop is similar to Chrome but includes an “Or” Version string.

Making statements based on opinion; back them up with references or personal experience. More than 2,100 enterprises around the world rely on Sumo Logic to build, run, and secure their modern applications and cloud infrastructures.

(Source: loumo.jp)

Other Articles You Might Be Interested In

01: Example User Agent String
02: Brave Browser Change User Agent
03: Brave Browser User Agent String
04: Brave Change User Agent
05: Brave User Agent String
06: Browser User Agent Identifier
07: Browser User Agent Info
08: Browser User Agent Online
09: Browser User Agent String Wireshark
10: Robots.txt User Agent
Sources
1 moz.com - https://moz.com/learn/seo/robotstxt
2 developers.google.com - https://developers.google.com/search/docs/advanced/robots/create-robots-txt
3 developers.google.com - https://developers.google.com/search/reference/robots_txt
4 qodeinteractive.com - https://qodeinteractive.com/magazine/wordpress-robots-txt-file/
5 ahrefs.com - https://ahrefs.com/blog/robots-txt/
6 yoast.com - https://yoast.com/ultimate-guide-robots-txt/
7 searchfacts.com - https://searchfacts.com/robots-txt-allow-disallow-all/
8 developers.google.com - https://developers.google.com/search/docs/advanced/crawling/overview-google-crawlers
9 www.robotstxt.org - http://www.robotstxt.org/robotstxt.html
10 stackoverflow.com - https://stackoverflow.com/questions/20294485/is-it-possible-to-list-multiple-user-agents-in-one-line