In the World Wide Web, a query string is the part of a URL that contains data to be passed to web applications such as CGI programs. Image:Url.png When a web page is requested via the Hypertext Transfer Protocol, the server locates a file in its file system based on the requested URL. This file may be a regular file or a program. In the second case, the server may (depending on its configuration) run the program, sending its output as the required page. The query string is a part of the URL which is passed to the program. Its use permits data to be passed from the HTTP client (often a browser) to the program which generates the web page.