is a technique on the World Wide Web in which a Uniform Resource Locator (URL) may be made substantially shorter in length and still direct to the required page. This is achieved by using an HTTP Redirect on a domain name that is short, which links to the web page that has a long URL. For example, the URL http://en.wikipedia.org/wiki/URL_shortening can be shortened to http://ipx.cc/8. This is especially convenient for messaging technologies such as Twitter and Identi.ca which severely limit the number of characters that may be used in a message. Short URLs allow otherwise long web addresses to be referred to in a tweet. In November 2009, the shortened links on one URL shortening service were accessed 2.1 billion times.
Another use of URL shortening is to disguise the underlying address. Although this may be desired for legitimate business or personal reasons, it is open to abuse and for this reason, some URL shortening service providers have found themselves on spam blacklists, because of the use of their redirect services by sites trying to bypass those very same blacklists. Some websites prevent short, redirected URLs from being posted.
There are several reasons to use URL shortening. The free hosting space provided by Internet Service Providers for its customers may generate an aesthetically unpleasing address. Many web developers pass descriptive attributes in the URL to represent data hierarchies, command structures, transaction paths or session information. This can result in hundreds of character long URLs which contain complex character patterns. Such URLs are difficult to memorize and manually reproduce. As a result, long URLs must be copied-and-pasted for reliability. Thus, short URLs may be more convenient for websites or hard copy publications (e.g. a printed magazine or a book), the latter often requiring that very long strings be broken into multiple lines (as is the case with some e-mail software or internet forums) or truncated.
On Twitter and some instant-messaging services, there is a limit to the number of characters a message can carry. Using a URL shortener can allow linking to web pages which would otherwise violate this constraint. Some shortening services, such as ipx.cc, can generate URLs that are human-readable, although the resulting strings are longer than those generated by a length-optimized service. Finally, URL shortening sites provide detailed information on the clicks a link receives, which can be simpler than setting up an equally powerful server-side analytics engine.
URLs encoded in two-dimensional barcodes such as QR code are often shortened by a URL shortener in order to reduce the printed area of the code or allow printing at lower density in order to improve scanning reliability.