The user agent o agent is the identifier or name with which a program logs in to the web server to request a document. The name is passed through the HTTP header. Software programs and search engine robots can be identified by this name.
The user agent allows to see precisely when a search engine robot visited the web portal, which can be useful for log file evaluation. The fact that the name can be freely selected raises the problem that robots can disguise themselves as other user agents. This allows the robot to identify, for example, spam websites. A bot with an incorrect identifier can check a web portal incognito, since the web server identifies it as a normal browser and not as a search engine bot.
How does it work
If a browser wants to enter a web page, the program tells the document when the request is made, which agent is used (Agent Name Delivery). The user agent identifier is a different information string. It contains the operating system as well as the version of the operating system or the name of the product.
If during this procedure the program provides the next identification, for example:
Mozilla / 5.0 (Windows; U; Windows NT 5.1; de-DE; rv; 1.7.6) Gecko / 20050226 Firefox / 1.0.1
means the user used Mozilla Firefox version 1.0.1 with Windows XP operating system and German language pack. It is also possible to identify that the user used the Gecko rendering engine version 1.7.6, which was released on February 26, 2005.
User agent types
- Web browsers: Web browsers are programs used to surf the Internet. They allow you to view and run website graphics or applets. Examples of web browsers are Internet Explorer, Safari, Mozilla Firefox, or Opera.
- Web apps: These are programs used for content maintenance, communication or file execution, such as streaming (example: Spotify), video clips, Flash Player or Adobe Acrobat Reader.
- Spider (Crawler): Identifies search engine programs that regularly want new information and document changes on the Internet.
conclusion
In order for search engines to be able to display search results to a user, they have to search the web for content on a daily basis. Web servers, despite everything, cannot tell whether a person or a search engine robot visits a web page. User agents help the web server to distinguish between human users and search engine robots.
