URL shortening
URL shortening 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 a redirect on a domain name that is short, which links to the web page that has a long URL. For example, the URL "http://example.com/about/index.html" can be shortened to "http://vkok.pw/um92". This is especially convenient for messaging technologies that limit the number of characters that may be used in a message, such as SMS, and for reducing the amount of typing required if the reader is copying a URL from a print source. In November 2009, the shortened links of the URL shortening service Bitly were accessed 2.1 billion times.[1]
Other uses of URL shortening are to "beautify" a link, track clicks, or disguise the underlying address. Although disguising of the underlying address may be desired for legitimate business or personal reasons, it is open to abuse[2] 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, such as is.gd, prevent short, redirected URLs from being posted.
Purposes
There are several reasons to use URL shortening. Often regular unshortened links may be aesthetically unpleasing. Many web developers pass descriptive attributes in the URL to represent data hierarchies, command structures, transaction paths or session information. This can result in URLs that are hundreds of characters long and that contain complex character patterns. Such URLs are difficult to memorize, type-out or distribute. 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 goo.gl, tinyurl.com, and bit.ly 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.
Registering a short URL
An increasing number of websites are registering their own short URLs to make sharing SMS easier. This can normally be done online, at the web pages of a URL shortening service. Short URLs often circumvent the intended use of top-level domains for indicating the country of origin; domain registration in many countries requires proof of physical presence within that country, although a redirected URL has no such guarantee.
Free URL shortening
