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

User Agent Js

Christina Perez
• Sunday, 25 October, 2020
• 13 min read

To use this module in your application, simply write the following code – The very basic implementation of this module is to generate random user agents.

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Here, stringing() function will convert the JavaScript value into JSON. It takes three parameters, first one will be the value to be converted into JSON, the second parameter will be the replace function that will transform the result, and the third parameter will be for adding indentation, line-break characters so that the converted JSON string is easily readable.

Here, we have created an instance of an user agent with the properties as platform and deviceCategory. We are restricting it to use the Windows 64 platform and run only on desktop.

Then, we created an array of 50 more user agents with the same configurations. We can also apply a filter to our application and the returning user agent will be matched to the applied filter. We can also combine the filters and an array of configurations that are to be applied to the returning user agent.

See your article appearing on the GeeksforGeeks main page and help other Geeks. The specification asks browsers to provide as little information via this field as possible.

Also keep in mind that users of a browser can change the value of this field if they want (UA spoofing). Some Firefox extensions do that; however, this only changes the HTTP header that gets sent, and doesn't affect browser detection performed by JavaScript code.


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.

It’s all great if we just fetch HTML and parse it with cheerio. Now, we need to scrape a website with JS enabled, because website is doing black magic client side rendering.

We set up Puppeteer JS, open the browser, load webpage and get the data. Most of the time this will be enough, but sometimes websites will try to check if you are doing something you shouldn’t.

Platform: Mac Intel, Win32, Linux x86_x64, iPhone, Linux armv8l … products: · Safari, Chrome, Opera, Edge … gives 20030107 · Firefox gives 20100101 vendors: · Chrome, Opera … gives Google Inc. · Safari gives Apple Computer, Inc. · Firefox, Internet Explorer, Edge … gives empty string OSCP: only Firefox cutlass: only Internet Explorer We can open DevTools and go to “Network conditions” tab.

If a website is checking navigator object, we need to override those properties. One thing we can’t fake is communication with a service worker.

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Making statements based on opinion; back them up with references or personal experience. This is why regular user agent parsers have major issues because they will most likely parse out the wrong browser name or confuse the render engine version with the actual version of the browser.

The module has been developed with a benchmark driven approach. It has a pre-compiled library that contains all the Regular Expressions and uses deferred or on demand parsing for Operating System and device information.

All this engineering effort has been worth it as this benchmark shows : Installation is done using the Node Package Manager (NPM).

This will asynchronous load the database from the server and compile it to a proper JavaScript supported format. If it fails to compile or load it from the remote location it will just fall back silently to the shipped version.

If you want to use this feature you need to add yamlparser and request to your package.Jason The first argument should the user agent string that is known on the server from the req.headers.user agent header.

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This allows you to detect if the user is browsing the web using the Chrome Frame extension. The parser returns an Agent instance, this allows you to output user agent information in different predefined formats.

The parse method returns an Agent instance which contains all details about the user agent. This can be handy if you expect to parse a lot of user agent strings.

It uses the same arguments as the user agent.parse method and returns exactly the same result, but it's just cached. agent string).browser name; This API provides you with a quick and dirty browser lookup.

The Agent exposes the parsed out information from the user agent strings. This allows us to extend the agent with more methods that do not necessarily need to be in the core agent instance, allowing us to expose a plugin interface for third party developers and at the same time create a uniform interface for all versioning.

Major The major version number of the family, it defaults to 0. Minor The minor version number of the family, it defaults to 0. Patch The patch version number of the family, it defaults to 0. When you access those 2 properties the agent will do on demand parsing of the Operating System or/and Device information.

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Agent.agent(); Returns the family and version number concatenated in a nice human-readable string. Agent.version(); Returns the version of the browser in a human-readable string.

As it requires the server module to function you need to install it separately: Agent .OS is now an OperatingSystem instance with version numbers.

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.

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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.

puppeteer js medium

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.

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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). I have included a zip file with all the example source code at the start of this tutorial, so you don’t have to copy-paste everything… Or if you just want to dive straight in.


Download & Notes Mobile Detection Useful Bits & Links The End Click here to download the source code, I have released it under the MIT license, so feel free to build on top of it or use it in your own project. There are 3 examples in the zip file, 3-mobile-detect.html requires the mobile detect library, but is not included.

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