User agent

A user agent is a software application or script that is used to identify its underlying source to servers and other network-based systems on the internet. The user agent string typically contains information about the type of client, the operating system, the device, and the application or script that is making the request.

The user agent string is used by servers to provide different types of content, based on the user agent string that is provided. For example, if a server receives a request from a user agent that identifies itself as a mobile device, the server may provide a mobile-optimized version of the content.

User agents are typically found in a web browser as part of a request that is sent to a web server. The user agent string can be used to determine the client or browsing platform, such as Microsoft Internet Explorer, Google Chrome, Mozilla Firefox, Apple Safari, or Opera. It can also be used to determine the version of the client that is being used, and the operating system of the device that is making the request.

In addition to web browsers, user agents can also be found in other types of applications, such as email clients, search engines, and manipulation tools. It can also be found in web crawlers, or programs that are used to extract and analyze web content.

User agents are generally used to improve the user experience, but they can also be used by malicious agents to gain access to networks and maliciously modify content or perform other malicious activities.

In order to identify and differentiate different user agents, the World Wide Web Consortium (W3C) uses an international standard, known as the User Agent Identification Standard (UAIS). The standard defines the standard format for user agent strings and provides a platform for the development of agents that can be reliably identified.