URL shortening

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URL shortening is a technique on the World Wide Web in which a URL may be made substantially shorter in length. This involves using an HTTP Redirect on a domain name that is short to link to a website which has a long URL. Domain names are linked to IP addresses, however, in order to be human friendly, the Latin alphabet can be used. Sometimes this can lead to extremely long URLs. For example, the URL http://en.wikipedia.org/w/index.php?title=TinyURL&diff=283621022&oldid=283308287 can be shortened to http://tinyurl.com/mmw6lb

Contents 1 Purposes 1.1 Avoid URL garbling 1.2 Use the smallest space possible 1.3 Reading aloud 1.4 Manipulating visitors 2 Unsupported schemes 3 Techniques 4 History 5 Criticism and problems 5.1 Linkrot 5.2 Other issues 5.3 Blocking 6 See also 7 References 8 External links

[edit] Purposes

There are several reasons to use URL shortening:

[edit] Avoid URL garbling

Some web developers tend to pass descriptive attributes in the URL to represent data hierarchies, command structures, transaction paths and session information. This may result in a URL that is aesthetically unpleasant and difficult to remember. Copying a URL that is hundreds of characters long can make the URL garbled. Thus a short URL is more useful to copy from an e-mail message or forum post.

[edit] Use the smallest space possible

On Twitter and some instant messaging services, there is a total character limit to messages. Using a URL shortener can enable users to include a URL that would not fit. Tinyarro.ws and qoiob.com use Unicode characters to achieve the shortest URLs possible, since more shortened URLs are possible with a given number of characters compared to those using a standard Latin alphabet.^[1]

A QR Code that stores a URL can be made physically smaller (or more readable in the same size) by using a URL shortener to minimize a URL it encodes.^{[citation needed]}

[edit] Reading aloud

To accomplish this objective any URL shortening service can be useful. However those which let the user choose the URL are more suited for this task. Some shortening services, such as tinyurl.com and bit.ly, can generate URLs that are human-readable, though the resulting strings are longer than those generated by a length-optimized service.

[edit] Manipulating visitors

URL shortening is a special kind of URL redirection, which is sometimes used in pranks, phishing, or affiliate hiding. For example, a TinyURL link could redirect to the shock site goatse.cx in a prank. Some of these services (br.st, for example) have started filtering all shortened links through services like Google Safe Browsing.

[edit] Unsupported schemes

Most URI schemes are supported by URL shorteners, including http:, https:, ftp:, pop:, imap:, nntp:, news:, ldap:, gopher:, dict:, dns:, etc.

However, data: and javascript: URLs are not typically supported for security reasons.

[edit] Techniques

Every long URL is associated with a key, which is the part after http://domain.tld/. For example http://tinyurl.com/m3q2xt has a key of m3q2xt.

There are several techniques to implement a shortening.

• Keys can be generated numerically in base 36 assuming 26 letters and 10 numbers. The keys in order would be 0, 1, 2, ..., 9, a, b, ..., z. If uppercase and lowercase letters are accepted then the number should be in base 62 (26 + 26 + 10).
• A hash function can be made or a random number can be generated so that key sequence is not predictable
• Users can propose their own keys. For example, http://en.wikipedia.org/w/index.php?title=TinyURL&diff=283621022&oldid=283308287 can be shortened to http://tinyurl.com/w1k1t1ny.

For redirection techniques see URL redirection.

[edit] History

The idea of URL shortening dates to at least 2001.^[2] The first notable URL shortening service, TinyURL, was launched in 2002. Its popularity influenced the creation of at least 100 similar websites^[3] Most are simply domain alternatives

Initially Twitter automatically translated long URLs using TinyURL. As of 2009, it uses bit.ly.^[4]

In May 2009 .tk, which previously was used to generate memorable domains via URL redirection, launched tweak.tk,^[5] which generates very short URLs such as http://mxtux.tk/.

On 10 August 2009, tr.im, a notice shortening service announced that "[s]tatistics can no longer be considered reliable, or reliably available going forward" and that they were shuttering the generation of new shortened URLs, but assured existing tr.im short URLs would "continue to redirect, and will do so until at least December 31, 2009". A blog post on the site attributed this move to several factors, including the lack of suitable revenue generation mechanisms to cover ongoing hosting and maintenance costs, lack of interest among possible purchasers of the service, and Twitter's default use of the bit.ly shortener.^[6] This blog post also questioned whether other shortening services can successfully monetize URL shortening in the longer term. A few days later, tr.im reversed itself on this move, announcing it would resume all operations "going forward, indefinitely, while we continue to consider our options in regards to tr.im's future"^[7]

On 14 August 2009, WordPress announced the wp.me URL shortener for use when referring to any WordPress.com blog post.^[8]

In November 2009, shortened links on bit.ly were accessed 2.1 billion times.^[9] Around that time, bit.ly and TinyURL were the most widely used URL shortening services^[9]

In December 2009, the URL shortener TO./ NanoURL was launched by .TO. The service creates a URL address which looks like http://to./xxxx, where xxxx represents a combination of random numbers and letters. NanoURL currently generates the shortest URLs of all URL shortening services, because it is hosted on a top level domain (the one of Tonga). This rare form of URL may cause problems with some browsers, which interpret this as a search term and look it up on a search engine, instead of opening it.^[10]

On 14 December 2009, Google announced a service called Google URL Shortener, which is currently only available for use through Google products (such as Google Toolbar and Feedburner.)^[11] It does, however, have two extensions (standard and lite versions) for Google Chrome.^[12] On 21 December 2009, Google also announced a service called Youtube URL Shortener^[13]

[edit] Criticism and problems

The convenience offered by URL shortening also introduces potential problems, which have led to criticism of the use of these services.

[edit] Linkrot

Short URLs are subject to linkrot: In case the service stops working, all URLs related to the service will become broken. This problem is emphasized by the concern that many existing URL shortening services may not have a sustainable business model in the long term, which was highlighted by the statement from tr.im in August 2009 (see above)^[9] In fall 2009, the Internet Archive started the "301 Works" projects, together with (initially) 20 collaborating companies, whose short URLs will be preserved by the project.^[9]

[edit] Other issues

Users may be exposed to privacy issues in that the link shortening service is in a position to track a user's behaviour across many domains.

Short URLs add an additional layer of complexity, that is, every access requires more requests (at least one more DNS lookup and HTTP request).

A short URL obscures the target address, and as a result it's sometimes used to redirect to an unexpected site. Examples of this are rickrolling, redirecting to scam and affiliate websites, or shock sites; ZoneAlarm has given the warning "TinyURL may be unsafe. This website has been known to distribute spyware." TinyURL has countered this problem by offering an option to present a link when using TinyURL, instead of redirection.^[14] In addition, even if the link does not include a preview, the preview may still be accessed by simply prefixing the word "preview" to the front of the URL (Ex: http://tinyurl.com/8kmfp could be retyped as http://preview.tinyurl.com/8kmfp) to see where the link will lead. Not all protocols are shortened. Services such as Protocol Free URL Shortener made a difference in the way Protocol based URL's were being accessed. Protocols including http|https|ftp|ftps|mailto|news|mms|rtmp|rtmpt|e2dk started to be shortened by such services. Opaqueness is also used by spammers, who use such links in spam to bypass URL blacklists. TinyURL, in turn, disables spam-related links from redirecting.^[15]

[edit] Blocking

TinyURL is blocked in Saudi Arabia.^[16]

Some websites have responded by blocking short redirected URLs from being posted:

• In 2006, MySpace banned posting TinyURLs^{[citation needed]}
• Yahoo! Answers blocks postings that contain TinyURLs^{[citation needed]}
• In 2009, the Twitter network replaced TinyURL with Bit.ly as its default shortener of links longer than 26 characters^[4]
• Panera Bread blocks access to TinyURL within its free Wi-Fi network^[17]
• Craigslist does not appear to accept Bit.ly links in its posts.

Security professionals are also suggesting users to always preview the short URLs before accessing it, especially after the shortener service cli.gs got hacked, exposing millions of users.^[18]

[edit] See also

• Link rot
• TinyURL
• URL redirection

[edit] References

[edit] External links

• URL redirection and shortening at the Open Directory Project
• Comparison of URL Shortening services SearchEngineLand, April 2009
• Scott Nesbitt: Shorter is Sweeter: A Look at URL Shorteners Geeks.com, February 7, 2010
• The most comprehensive and ever-growing list of URL shortening services, June 7, 2010