{"id":30079,"date":"2024-11-12T12:39:29","date_gmt":"2024-11-12T12:39:29","guid":{"rendered":"https:\/\/www.seobility.net\/en\/blog\/wiki\/user-agent\/"},"modified":"2025-02-26T09:23:44","modified_gmt":"2025-02-26T09:23:44","slug":"User_Agent","status":"publish","type":"wiki","link":"https:\/\/www.seobility.net\/en\/wiki\/User_Agent","title":{"rendered":"User Agent"},"content":{"rendered":"

Definition<\/span><\/h2>\n

A user agent (short: UA) is software that communicates with servers in a network. An example would be a web browser that retrieves a web page from a server on the internet and displays it. The user agent acts as a mediator between the user and the web server just like a human agent. It processes the user’s instructions, transfers them and receives the requested data. The user agent transmits information such as the browser version, installed plugins<\/a>, and other data to the web server. Based on this data, the server can assess the capabilities of the user agent and deliver the appropriate data to it.\n<\/p>\n

Transmitting the user agent through the HTTP header<\/span><\/h2>\n
\n
\"User-Agent\"<\/a> <\/p>\n
Figure:<\/b> User Agent – Author: Seobility – License: CC BY-SA 4.0<\/a><\/div>\n<\/div>\n<\/div>\n

The information that identifies the user agent is transferred to the web server in the HTTP request header<\/a>. Each header contains a characteristic string that servers can use to identify the application type, operating system, software vendor, or software version of the requesting user agent.\n<\/p>\n

The structure and content of this information are not standardized. Each developer can insert and submit his own information. For example, the basic syntax for a Firefox web browser is:\n<\/p>\n

Mozilla\/5.0 (platform; rv:geckoversion) Gecko\/geckotrail Firefox\/firefoxversion<\/pre>\n
Mozilla\/5.0<\/i> is a general token stating the web browser is compatible with Mozilla. Modern browsers use this token for historical reasons only, since it is no longer of great importance.\n<\/p>\n
platform<\/i> describes the native platform the web browser operates on – for example, Windows, Mac, Linux or Android and whether it is a mobile phone or not. Firefox OS for mobile simply puts the word “Mobile” here.\n<\/p>\n
rv:geckoversion<\/i> indicates the version of Gecko. Gecko is an HTML rendering<\/a> engine that web browsers use to display a web page. In current browsers, geckoversion is the same as firefoxversion.\n<\/p>\n
Gecko\/geckotrail<\/i> indicates that the browser is based on Gecko. On desktop, geckotrail has the fixed string “20100101”.\n<\/p>\n
Firefox\/firefoxversion<\/i> indicates the browser is a Firefox version with the specified version number.\n<\/p>\n
An example of a Firefox browser on a desktop operating on Windows would look like this:\n<\/p>\n
Mozilla\/5.0 (Windows NT 6.1; Win64; x64; rv:64.0) Gecko\/20100101 Firefox\/64.0<\/pre>\n
Information provided by the agent can be modified or falsified. One example would be some mobile web browsers, which can switch between mobile or desktop mode to get access to websites that only allow desktop computers.
\nIn the early days of the internet, Microsoft’s first Internet Explorer pretended to be a Netscape browser to access web pages designed for Netscape Navigator, the dominant browser on the market back then.\n<\/p>\n
Types of user agents<\/span><\/h2>\n
Browsers like Mozilla Firefox, Google\u2019s Chrome as well as Safari and Opera are examples of user agents. However, other applications can also act as user agents. Examples are:\n<\/p>\n