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/
Your browser sends the user agent to every website you connect to. There is no conventional way of writing an user agent string as different browsers use different formats and many web browsers load a lot of information onto their user agents.
Google Chrome Internet Explorer Firefox Safari Opera See your article appearing on the GeeksforGeeks main page and help other Geeks.
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.
This feature is useful for SEO professionals, for example, to identify issues with cloaking which is against Google’s Webmaster Guidelines or auditing websites which has different look depending on the device. User agent is an HTTP request header string identifying browser, application, operating system which connects to the server.
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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. Following is the example of the user agent of Google Chrome version 69 running on Windows 10.
You might be wondering, why is the user agent of Google Chrome on Windows 10 so complicated? 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.
The most robust way to do it is with curl and based on how complex the query is, maybe your only option. Yes, this function also opens files from URLs, assuming the option is enabled in the config.
Including headers is something that is fairly easy to do, but it is not entirely straight forward with PHP. This guide will show you how to set a custom useragentheader to PHP HTTP requests.
As a quick recap, an user agent is a string that is sent as a header in an HTTP request. It is never wise to build security based on this alone, but if you want to block bots, the user agent is usually the place to start.
The code below will show you a fairly simple curl request that has a custom user agent defined. On top of being able to fetch HTML, JSON or any format from a URL, you can also pass headers in this request.
The templates for the Amazon Silk user agents are shown below. The version can change whenever the Fire device receives a software update.
Unless you want to provide a unique experience for different Kindle Fire devices, we recommend a general match that will work over time as product models and version numbers change. The following examples illustrate best practices for matching the Amazon Silk user agent across Kindle Fire device types.
You can use user agent detection to target content, but this approach can be problematic. Those variables will change over time, so user agent detection isn't future proof.
navigator.sergeant : This method reads the navigator object when the page load is finished. navigator.sergeant : This method clones the “navigator” object exactly when page is about to render to prevent any external scripts from altering it later.
Tab : Could be one of “navigator”, “UA_prayer”, “platform_JS” which indicates the default rendering engine that is used to display the results. Verbose : Could be one of “true” or “false” values which indicates whether the page uses all methods or just the active one.
User agents are the strings of text which specify the browser and operating system of web servers. User agents are present in HTTP headers when the browser wants to communicate with a server.
Each browser has its specific user agent string and web servers utilize this information to deliver appropriate material across different operating systems. An example of this is the mobile version of webpages in devices; usually slimmed down and organized vertically for user ease.
Web servers provide the bots with special treatments and verifications such as mandatory registrations, screens, etc. Mozilla was considerably more advanced in terms of connectivity and security than Mosaic because of the ease of supported frames it provided.
This was a remarkable advancement considering the other browsers made use of sending old pages without any frames at all. However, there was still no receiving end of webpages with frames, because they were just shared with Mozilla browsers.