View source for URL shortening

{{Short description|Web technique}}
{{pp-pc}}
{{Self-reference|For information about short URLs for pages on Wikipedia, see [[Wikipedia:URLShortener]].}}
{{more citations needed|date=July 2014}}
{{Use dmy dates|date=November 2021}}
[[File:Screenshot URL shortener.png|thumb|upright=1.5|The [[m:Special:UrlShortener|URL shortener]] on [[Meta-Wiki]]]]
'''URL shortening''' is a technique on the [[World Wide Web]] in which a [[Uniform Resource Locator]] (URL) may be made substantially shorter and still direct to the required page. This is achieved by using a [[URL redirection|redirect]] which links to the [[web page]] that has a long URL. For example, the URL "{{mono|<nowiki>https://en.wikipedia.org/wiki/URL_shortening</nowiki>}}" can be shortened to "{{mono|<nowiki>w.wiki/U</nowiki>}}". Often the redirect [[domain name]] is shorter than the original one. A [[semantic URL|friendly URL]] may be desired for messaging technologies that limit the number of [[Character (computing)|characters]] in a message (for example SMS), for reducing the amount of typing required if the reader is copying a URL from a print source, for making it easier for a person to remember, or for the intention of a [[permalink]]. In November 2009, the shortened links of the URL shortening service [[Bitly]] were accessed 2.1 billion times.<ref>[http://bits.blogs.nytimes.com/2009/12/14/googl-challenges-bitly-as-king-of-the-short/ Goo.gl Challenges Bit.ly as King of the Short] {{Webarchive|url=https://web.archive.org/web/20110710201651/http://bits.blogs.nytimes.com/2009/12/14/googl-challenges-bitly-as-king-of-the-short/ |date=10 July 2011 }} – New York Times, 14 December 2009</ref>

Other uses of URL shortening are to "beautify" a link, track clicks, or disguise the underlying address. This is because the URL shortener can redirect to just about any web domain, even malicious ones. So, although disguising of the underlying address may be desired for legitimate business or personal reasons, it is open to abuse.<ref name="twitter">{{cite news|last1=Curtis|first1=Sophie|title=Twitter's t.co URL shortener used to spread spam|url=https://www.telegraph.co.uk/technology/internet-security/11020760/Twitters-t.co-URL-shortener-used-to-spread-spam.html|website=[[The Daily Telegraph]]|access-date=15 March 2015|date=8 August 2014|archive-url=https://web.archive.org/web/20150403025200/http://www.telegraph.co.uk/technology/internet-security/11020760/Twitters-t.co-URL-shortener-used-to-spread-spam.html|archive-date=3 April 2015|url-status=live}}</ref> Some URL shortening service providers have found themselves on spam [[blocklist]]s, because of the use of their redirect services by sites trying to bypass those very same blocklists. Some websites 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 forum]]s) or truncated.

On [[Twitter]] and some [[instant messaging]] services, there is a limit to the number of characters a message can carry{{spaced endash}} however, Twitter now shortens links automatically using its own URL shortening service, {{mono|[[t.co]]}}, so there is no need to use a separate URL shortening service just to shorten URLs in a tweet. On other such services, using a URL shortener can allow linking to web pages which would otherwise violate this constraint. Some shortening services, such as {{mono|[[goo.gl]]}}, {{mono|[[TinyURL|tinyurl.com]]}}, and {{mono|[[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, and unlike the latter, does not require any access to the server.

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==
Some websites create short links to make sharing links via instant messaging easier, and to make it cheaper to send them via SMS. This can be done online, at the web pages of a URL shortening service; to do it in batch via bulk upload with tools like CSV importer or on demand may require the use of an [[API]].

A few well-known websites have set up their own URL shortening services for their own use{{spaced ndash}} for example, Twitter with t.co,<ref>{{Cite web |title=t.co links |url=https://developer.twitter.com/en/docs/tco |access-date=2022-05-10 |website=developer.twitter.com |language=en |archive-date=27 April 2022 |archive-url=https://web.archive.org/web/20220427123733/https://developer.twitter.com/en/docs/tco |url-status=live }}</ref> Telegram with t.me, Google with g.co,<ref>{{Cite web |title=g.co |url=https://g.co/ |access-date=2022-05-10 |website=g.co |language=en |archive-date=14 January 2019 |archive-url=https://web.archive.org/web/20190114181700/https://g.co/ |url-status=live }}</ref> and GoDaddy with x.co.<ref>{{Cite web |title=URL Shortener |url=https://shortener.godaddy.com/ |access-date=2022-05-10 |website=shortener.godaddy.com |archive-date=3 May 2022 |archive-url=https://web.archive.org/web/20220503033123/https://shortener.godaddy.com/ |url-status=live }}</ref>

==Techniques==
{{See also|URL redirection}}
In URL shortening, every long URL is associated with a [[unique key]], which is the part after its [[top-level domain name]]. For example, {{mono|<nowiki>https://tinyurl.com/m3q2xt</nowiki>}} has a key of {{mono|m3q2xt}}, these keys are case-sensitive most of the time and using the wrong case may lead to a different destination URL. Not all redirection is treated equally; the redirection instruction sent to a browser can contain in its header [[List of HTTP status codes|HTTP response status codes]] such as 301 (moved permanently), 302 (found), 307 (temporary redirect) or 308 (permanent redirect).

There are several techniques to implement URL shortening. Keys can be generated in [[base 36]], assuming 26 letters and 10 numbers. In this case, each character in the sequence will be {{mono|0, 1, 2, ..., 9, a, b, c, ..., y, z}}. Alternatively, if uppercase and lowercase letters are differentiated, then each character can represent a single digit within a number of [[base 62]] (26 + 26 + 10). In order to form the key, a [[hash function]] can be made, or a [[random number generation|random number generated]] so that key sequence is not predictable. Or users may propose their own custom keys. For example, {{mono|<nowiki>https://example.com/product?ref=01652&type=shirt</nowiki>}} can be shortened to {{mono|<nowiki>https://tinyurl.com/exampleshirt</nowiki>}}.

Not all URI schemes are capable of being shortened as of 2011, although URI schemes such as {{mono|http}}, {{mono|https}}, {{mono|ftp}}, {{mono|ftps}}, {{mono|mailto}}, {{mono|mms}}, {{mono|rtmp}}, {{mono|rtmpt}}, {{mono|ed2k}}, {{mono|pop}}, {{mono|imap}}, {{mono|nntp}}, {{mono|news}}, {{mono|ldap}}, {{mono|gopher}}, {{mono|dict}} and {{mono|dns}} are being addressed by such services as URL shorteners. Typically, [[Data URI scheme|{{mono|data:}}]] and {{mono|javascript:}} URLs are not supported for security reasons (to combat attacks like [[cross-site scripting]] and [[session hijacking]]). Some URL shortening services support the forwarding of {{mono|mailto}} URLs, as an alternative to [[address munging]], to avoid unwanted harvest by [[web crawlers]] or [[Internet bot|bots]]. <!-- [ The reference given for the following sentence does *not* show that CAPTCHAs are used protect mail forwarding URLs, it does not talk about mailto URLs at all. Concerning CAPTCHAs, the reference says that "little security such as CAPTCHAs is used": ] --> This may sometimes be done using short, [[CAPTCHA]]-protected URLs, but this is not common.<!-- Does this edit address the previous concern? Richard asr --><ref>{{cite web|url=http://certmag.com/spammers-storm-url-shortening-services/|title=Spammers Storm URL Shortening Services|date=17 August 2009|publisher=CertMag|url-status=live|archive-url=https://web.archive.org/web/20191101070103/http://certmag.com/spammers-storm-url-shortening-services/|archive-date=1 November 2019}}</ref>

Makers of URL shorteners usually register domain names with less popular or esoteric [[Top-level domain]]s in order to achieve a short URL and a catchy name, often using [[domain hack]]s.
This results in registration of different URL shorteners with a myriad of different countries, leaving no relation between the country where the domain has been registered and the URL shortener itself or the shortened links. [[Top-level domain]]s of countries such as [[Libya]] ([[.ly]]), [[Samoa]] ([[.ws]]), [[Mongolia]] ([[.mn]]), [[Malaysia]] ([[.my]]) and [[Liechtenstein]] ([[.li]]) have been used as well as many others. In some cases, the political or cultural aspects of the country in charge of the [[TLD|top-level domain]] may become an issue for users and owners,<ref>{{cite web |url=http://blog.hootsuite.com/li-ly-url-shortener/ |title=#HootSuite Offers Choice of URL Shorteners ~ From Libya to Liechtenstein – HootSuite Social Media Management |publisher=Blog.hootsuite.com |access-date=20 April 2013 |archive-url=https://web.archive.org/web/20130614151108/http://blog.hootsuite.com/li-ly-url-shortener/ |archive-date=14 June 2013 |url-status=live }}</ref> but this is not usually the case.

Services may record inbound statistics, which may be viewed publicly by others.<ref name="zdnet chapman 2012">{{cite news|last=Chapman|first=Stephen|title=How to spy on campaigns of competitors who use URL shorteners|url=https://www.zdnet.com/article/how-to-spy-on-campaigns-of-competitors-who-use-url-shorteners/|access-date=10 September 2012|newspaper=[[ZDNet]]|date=28 August 2012|archive-url=https://web.archive.org/web/20120902091730/http://www.zdnet.com/how-to-spy-on-campaigns-of-competitors-who-use-url-shorteners-7000001088/|archive-date=2 September 2012|url-status=live}}</ref>

==Expiry and time-limited services==
While many providers claim their shortened URLs won't expire for as long as the service is provided, they may decide to discontinue the service at any time.

A permanent URL is not necessarily a good thing. There are security implications, and obsolete short URLs remain in existence and may be circulated long after they cease to point to a relevant or even extant destination. Sometimes a short URL is useful simply to give someone over a telephone conversation for a one-off access or file download, and no longer needed within a couple of minutes.

Some providers offer expiration on shortened URLs. This may include URLs that expire after a certain amount of time, on a certain date or after a certain number of usages.{{Citation needed|date=July 2022}}

A Microsoft Security Brief recommends the creation of short-lived URLs, but for reasons explicitly of security rather than convenience.<ref>{{cite web | url=http://msdn.microsoft.com/en-us/magazine/dd458793.aspx | title=Protect Your Site With URL Rewriting – A Stateless Approach: Automatically Expiring URLs | publisher=Microsoft MSDN Magazine | work=Security Briefs | date=March 2009 | access-date=1 August 2013 | author=Sullivan, Bryan | archive-url=https://web.archive.org/web/20130717081358/http://msdn.microsoft.com/en-us/magazine/dd458793.aspx | archive-date=17 July 2013 | url-status=live }}</ref>

==History==
An early reference is US Patent [http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6957224.PN.&OS=PN/6957224&RS=PN/6957224 6957224], which describes <blockquote>...a system, method and computer program product for providing links to remotely located information in a network of remotely connected computers. A uniform resource locator (URL) is registered with a server. A shorthand link is associated with the registered URL. The associated shorthand link and URL are logged in a registry database. When a request is received for a shorthand link, the registry database is searched for an associated URL. If the shorthand link is found to be associated with a URL, the URL is fetched, otherwise an error message is returned.<ref>
{{US patent reference
 | number = 6957224
 | y = 2005
 | m = 10
 | d = 18
 | inventor = Nimrod Megiddo and Kevin S. McCurley; assigned to IBM corp.
 | title = Efficient retrieval of uniform resource locators
}}
</ref></blockquote>
The patent was filed in September 2000; while the patent was issued in 2005, US patent applications are made public within 18 months of filing.

Another reference to URL shortening was in 2001.<ref>[http://www.metafilter.com/8916/ "Comment thread 8916"] {{Webarchive|url=https://web.archive.org/web/20090905013027/http://www.metafilter.com/8916/ |date=5 September 2009 }}. ''[[Metafilter]]''. 10 June 2001; Announcement of URL shortening service available at makeashorterlink.com</ref> The first notable URL shortening service, [[TinyURL]], was launched in 2002. Its popularity influenced the creation of at least 100 similar websites,<ref>[http://code.google.com/p/shortenurl/wiki/URLShorteningServices "URL Shortening Services"] {{Webarchive|url=https://web.archive.org/web/20100103163826/http://code.google.com/p/shortenurl/wiki/URLShorteningServices |date=3 January 2010 }} shortenurl – Supported URL shortening services</ref> although most are simply domain alternatives. Initially, [[Twitter]] automatically translated URLs longer than twenty-six characters using TinyURL, although it began using bit.ly instead in 2009<ref name="nytbitly">Wortham, Jenna (7 May 2009) [http://bits.blogs.nytimes.com/2009/05/07/bitly-eclipses-tinyurl-on-twitter/ "Bit.ly Eclipses TinyURL on Twitter"] {{Webarchive|url=https://web.archive.org/web/20101123100345/http://bits.blogs.nytimes.com/2009/05/07/bitly-eclipses-tinyurl-on-twitter/ |date=23 November 2010 }} ''Bits'' ([[blog]] at ''[[The New York Times]]''). Retrieved 1 January 2011.</ref> and later developed its own URL shortening service, t.co.

On 14 August 2009 [[WordPress]] announced the ''wp.me'' URL shortener for use when referring to any WordPress.com blog post.<ref>[http://en.blog.wordpress.com/2009/08/14/shorten/ "WP.me – Shorten Your Links"] {{Webarchive|url=https://web.archive.org/web/20090818141625/http://en.blog.wordpress.com/2009/08/14/shorten/ |date=18 August 2009 }} [[WordPress]]. 14 August 2009.</ref> In November 2009, shortened links on ''[[bit.ly]]'' were accessed 2.1 billion times.<ref name="times">Ahmed, Murad (7 December 2009). [https://www.thetimes.com/article/new-project-in-scramble-to-save-vanishing-internet-links-dqp6hk2cjfd "New Project in Scramble To Save Vanishing Internet Links – The Internet Archive Is Fighting To Preserve Shortened Web Links Created by Free Online Services That May Be Running Out of Money"] . ''[[The Times]]''. Retrieved 1 January 2011.</ref> Around that time, ''bit.ly'' and ''TinyURL'' were the most widely used URL-shortening services.<ref name=times/>

One service, tr.im, stopped generating short URLs in 2009, blaming a lack of revenue-generating mechanisms to cover costs and Twitter's default use of the ''bit.ly'' shortener, and questioning whether other shortening services could be profitable from URL shortening in the longer term.<ref>[https://web.archive.org/web/20090810234517/http://blog.tr.im/post/159369789/tr-im-r-i-p tr.im R.I.P.] blog.tr.im</ref> It resumed for a time,<ref>[https://web.archive.org/web/20090813014303/http://blog.tr.im/post/160697842/tr-im-resurrected tr.im Resurrected]. blog.tr.im</ref> then closed.

The shortest possible long-term URLs were generated by NanoURL from December 2009 until about 2011, associated with the [[Top-level domain|top-level]] ''.to'' (Tonga) domain, in the form {{mono|<nowiki>http://to./xxxx</nowiki>}}, where {{mono|<nowiki>xxxx</nowiki>}} represents a sequence of random numbers and letters.<ref>{{cite web |last=Michlick |first=Frank |url=http://www.domainnamenews.com/cctlds/worlds-shortest-url-shortener/6741 |title=.TO ccTLD Becomes Worlds Shortest URL Shortener |publisher=Domainnamenews.com |access-date=20 April 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130503173537/http://www.domainnamenews.com/cctlds/worlds-shortest-url-shortener/6741 |archive-date=3 May 2013 }}</ref>

On 14 December 2009 [[Google]] announced a service called Google URL Shortener at goo.gl, which originally was only available for use through Google products (such as [[Google Toolbar]] and [[FeedBurner]])<ref name="GoogleShorter">{{cite web |last=Muthusrinivasan |first=Muthu |url=http://googleblog.blogspot.com/2009/12/making-urls-shorter-for-google-toolbar.html |title=Making URLs Shorter for Google Toolbar and FeedBurner |publisher=Googleblog.blogspot.com |date=14 December 2009 |access-date=20 April 2013 |archive-url=https://web.archive.org/web/20130531062301/http://googleblog.blogspot.com/2009/12/making-urls-shorter-for-google-toolbar.html |archive-date=31 May 2013 |url-status=live }}</ref> and extensions for [[Google Chrome]].<ref name="goo.gl URL Shortener">{{cite web |url=https://chrome.google.com/extensions/detail/iblijlcdoidgdpfknkckljiocdbnlagk |title=goo.gl "URL Shortener – Google Chrome Extension Gallery" |access-date=20 April 2013 |archive-url=https://web.archive.org/web/20110412103736/https://chrome.google.com/extensions/detail/iblijlcdoidgdpfknkckljiocdbnlagk |archive-date=12 April 2011 |url-status=live }}</ref> On 21 December 2009, Google introduced a [[YouTube]] URL Shortener, youtu.be.<ref>{{cite web|url=http://youtube-global.blogspot.com/2009/12/make-way-for-youtube-links.html|title=Official YouTube Blog: Make Way for youtu.be Links|work=Official YouTube Blog|access-date=24 December 2009|archive-url=https://web.archive.org/web/20091225183142/http://youtube-global.blogspot.com/2009/12/make-way-for-youtube-links.html|archive-date=25 December 2009|url-status=live}}</ref> From September 2010 [[Google URL Shortener]] became available via a direct interface. The goo.gl service provides analytics details and a QR code generator.{{citation needed|date=February 2017}} On 30 March 2018 [[Google]] announced that it is "turning down support for goo.gl over the coming weeks and replacing it with [[Firebase#Firebase Dynamic Links|Firebase Dynamic Links]]" (although existing goo.gl links will continue to function).<ref>{{cite web|last1=Hermanto|first1=Michael|title=Transitioning Google URL Shortener to Firebase Dynamic Links|url=https://developers.googleblog.com/2018/03/transitioning-google-url-shortener.html|website=Google Developers|access-date=1 April 2018|archive-url=https://web.archive.org/web/20180630214043/https://developers.googleblog.com/2018/03/transitioning-google-url-shortener.html|archive-date=30 June 2018|url-status=live}}</ref> On July 18, 2024, Google announced that existing Google URL shortener URLs will stop working as of August 25, 2025. Google will add an interstitial page to warn users about this starting August 23, 2024.<ref>{{cite web |title=Google URL Shortener links will no longer be available |url=https://developers.googleblog.com/en/google-url-shortener-links-will-no-longer-be-available/ |website=developers.googleblog.com |publisher=Google |access-date=18 July 2024 |language=en}}</ref>

==Advantages==
The main advantage of a short link is its brevity. Depending on the transcription used, it might be more easily communicated and entered without error. To some extent it can obscure the destination of the URL; this may be advantageous, disadvantageous, or irrelevant.

==Disadvantages==
Short URLs often circumvent the intended use of [[top-level domain]]s 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.

===Abuse===
URL shortening may be utilized by [[spamming|spammers]] or for illicit internet activities.  As a result, many have been removed from online registries or shut down by web hosts or internet service providers.

According to Tonic Corporation, the registry for .to domains, it is "very serious about keeping domains spam free" and may remove URL shortening services from their registry if the service is abused.<ref>{{cite web |url=http://www.tonic.to/faq.htm |title=Tonic Corporation Frequently asked questions |publisher=Tonic.to |access-date=20 April 2013 |archive-url=https://web.archive.org/web/20130719213004/http://www.tonic.to/faq.htm |archive-date=19 July 2013 |url-status=live }}</ref>

In addition, "u.nu" made the following announcement upon closing operations:

<blockquote> The last straw came on September 3, 2010, when the server was disconnected without notice by our hosting provider in response to reports of a number of links to child pornography sites.  The disconnection of the server caused us serious problems, and to be honest, the level and nature of the abuse has become quite demoralizing. Given the choice between spending time and money to find a different home, or just giving up, the latter won out.<ref><nowiki>http://u.nu/unu-discontinued</nowiki> "u.nu :: discontinued."</ref></blockquote>

Google's url-shortener discussion group has frequently included messages from frustrated users reporting that specific shortened URLs have been disabled after they were reported as spam.<ref>{{cite web |url=https://groups.google.com/forum/?fromgroups#!topic/google-url-shortener/pemNrYhHZz8 |title=Google Discussiegroepen |access-date=20 April 2013 |archive-url=https://web.archive.org/web/20190708011907/https://groups.google.com/forum/?fromgroups#!topic/google-url-shortener/pemNrYhHZz8 |archive-date=8 July 2019 |url-status=live }}</ref>

A study in May 2012 showed that 61% of URL shorteners had shut down (614 of 1002).<ref>{{cite web |url=http://yi.tl/pages/urlshorteners.php |title=Ultimate list of URL shorteners |publisher=Yi.tl |date=23 May 2012 |access-date=20 April 2013 |archive-url=https://archive.today/20130418171155/http://yi.tl/pages/urlshorteners.php |archive-date=18 April 2013 |url-status=dead }}</ref> The most common cause cited was abuse by spammers.

===Linkrot===
The convenience offered by URL shortening also introduces potential problems, which have led to criticism of the use of these services. Short URLs, for example, will be subject to [[linkrot]] if the shortening service stops working; all URLs related to the service will become broken. It is a legitimate concern that many existing URL shortening services may not have a sustainable business model in the long term.<ref name=times/> In late 2009, the [[Internet Archive]] started the "301 Works" projects,<ref>{{cite web|url=https://archive.org/details/301works|title=301Works.org : Free Software : Download & Streaming : Internet Archive|work=archive.org|access-date=19 August 2016|archive-url=https://web.archive.org/web/20161001170944/https://archive.org/details/301works|archive-date=1 October 2016|url-status=live}}</ref> together with twenty collaborating companies (initially), whose short URLs will be preserved by the project.<ref name=times/>

===Transnational law===
Shortened internet links typically use [[Country code top-level domain|ccTLD]] domains, and are therefore often under the jurisdiction of a nation other than where the service provider is located. [[Libya]], for instance, exercised its control over the .ly domain in October 2010 to shut down vb.ly for violating Libyan pornography laws. Failure to predict such problems with URL shorteners and investment in URL shortening companies may reflect a lack of [[due diligence]].<ref>{{cite news|author=Staff writer|author-link=Staff writer|date=14 October 2010|title=Law, Politics and Internet Addresses – Tough.ly/Treated – Shortened Web Links Are Convenient, But They Come at a Price|newspaper=[[The Economist]]|url=https://www.economist.com/node/17249654|access-date=1 January 2010|archive-url=https://web.archive.org/web/20101017094610/http://www.economist.com/node/17249654|archive-date=17 October 2010|url-status=live}}</ref>

===Blocking and banning===
Some websites prevent short, redirected URLs from being posted.

In April 2009, TinyURL was reported to be blocked in [[Saudi Arabia]].<ref>{{cite web|url=http://committeetoprotectbloggers.org/2009/04/16/tinyurl-blocked-in-saudi-arabia/|title=TinyURL Blocked in Saudi Arabia|date=16 April 2009|publisher=Committee to Protect Bloggers|url-status=live|archive-url=https://web.archive.org/web/20090419232449/http://committeetoprotectbloggers.org/2009/04/16/tinyurl-blocked-in-saudi-arabia/|archive-date=19 April 2009}}</ref> [[Yahoo! Answers]] blocks postings that contain TinyURLs,{{citation needed|date=October 2014}} and [[Wikipedia]] does not accept links by any URL shortening services in its articles.<ref name="meta.wikimedia">{{cite web |url = https://meta.wikimedia.org/wiki/Spam_blacklist |title = Spam blacklist |work = meta.wikimedia.org |publisher = Meta, discussion about Wikimedia projects |access-date = 4 November 2016 |archive-url = https://web.archive.org/web/20170320034054/https://meta.wikimedia.org/wiki/Spam_blacklist |archive-date = 20 March 2017 |url-status = live }}</ref> The [[Reddit]] community strongly discourages{{px2}}{{mdash}}{{spaces|2|hair}}and in some subreddits, outright bans{{px2}}{{mdash}}{{spaces|2|hair}}URL shortening services for link submissions, because they disguise the origin domain name and whether the link has previously been submitted to Reddit, and there are few or no legitimate reasons to use link shorteners for Reddit link submissions.<ref>{{cite web|url=https://www.reddit.com/wiki/reddiquette|title=Rediquette|access-date=9 February 2017|archive-url=https://web.archive.org/web/20170208172336/https://www.reddit.com/wiki/reddiquette|archive-date=8 February 2017|url-status=live}}</ref>

===Privacy and security===
A short URL obscures the target address and can be used to redirect to an unexpected site. Examples of this are "[[rickrolling]]", and redirecting to [[shock site]]s, or to affiliate websites. The short URL can allow blocked URLs to be accessed, bypassing site [[blocklist]]s; this facilitates redirection of a user to blocked scam pages or pages containing malware or XSS attacks. TinyURL tries to disable spam-related links from redirecting.<ref>[[Brian Krebs|Krebs, Brian]] (13 June 2006). [https://web.archive.org/web/20061116192105/http://blog.washingtonpost.com/securityfix/2006/06/spam_spotted_using_tinyurl.html "Spam Spotted Using TinyURL"]. ''Security Fixes'' ([[blog]] at ''[[The Washington Post]]''). Retrieved 1 January 2011.</ref> [[ZoneAlarm]], however, has warned its users: "TinyURL may be unsafe. This website has been known to distribute spyware." TinyURL countered this problem by offering an option to view a link's destination before using a shortened URL. This ability is installed on the browser via the TinyURL website and requires the use of cookies.<ref>{{cite web |url=http://tinyurl.com/preview.php |title=Preview a TinyURL |publisher=Tinyurl.com |access-date=20 April 2013 |archive-url=https://web.archive.org/web/20130420105705/http://tinyurl.com/preview.php |archive-date=20 April 2013 |url-status=live }}</ref> A destination preview may also be obtained by prefixing the word "preview" to the URL of the TinyURL; for example, the destination of {{mono|<nowiki>https://tinyurl.com/8kmfp</nowiki>}} is revealed by entering {{mono|<nowiki>https://preview.tinyurl.com/8kmfp</nowiki>}}. Other URL shortening services provide a similar destination display.<ref>{{cite web |url=http://security.thejoshmeister.com/2009/04/how-to-preview-shortened-urls-tinyurl.html |title=the JoshMeister on Security: How to Preview Shortened URLs (TinyURL, bit.ly, is.gd, and more) |publisher=Security.thejoshmeister.com |date=11 April 2009 |access-date=20 April 2013 |archive-url=https://web.archive.org/web/20140325150505/http://security.thejoshmeister.com/2009/04/how-to-preview-shortened-urls-tinyurl.html |archive-date=25 March 2014 |url-status=live }}</ref> Security professionals suggest that users check a short URL's destination before accessing it,<ref>{{Cite web |last=University |first=Carnegie Mellon |title=Shortened URL Security - Information Security Office - Computing Services - Carnegie Mellon University |url=http://www.cmu.edu/iso/aware/dont-take-the-bait/shortened-url-security.html |access-date=2022-07-26 |website=www.cmu.edu |language=en |archive-date=1 June 2022 |archive-url=https://web.archive.org/web/20220601175226/https://www.cmu.edu/iso//aware/dont-take-the-bait/shortened-url-security.html |url-status=live }}</ref> following an instance where the shortening service cli.gs was compromised, exposing millions of users to security uncertainties.<ref>[https://web.archive.org/web/20090628221947/http://blog.cli.gs/news/cligs-got-hacked-restoration-from-backup-started "Updated: Cligs Got Hacked – Restoration from Backup Started"] [[Blog]] at [[Cli.gs]] (16 June 2009).</ref> There are several web applications that can display the destination URL of a shortened URL.{{citation needed|date=February 2017}}

Some URL shortening services filter their links through bad-site screening services such as [[Google Safe Browsing]]. Many sites that accept user-submitted content block links, however, to certain domains in order to cut down on spam, and for this reason, known URL redirection services are often themselves added to spam blocklists.

Another privacy problem is that many services' shortened URL format is small enough that it is vulnerable to brute-force search.  Many people use URL shorteners when they share links to private content, and in fact many web services like Google Maps have offered automatic generation of shortened links for driving directions that reveal personal information like home addresses and sensitive destinations like "clinics for specific diseases (including cancer and mental diseases), addiction treatment centers, abortion providers, correctional and juvenile detention facilities, payday and car-title lenders, gentlemen's clubs, etc."<ref>{{Cite web |url=https://freedom-to-tinker.com/blog/vitaly/gone-in-six-characters-short-urls-considered-harmful-for-cloud-services/ |title=Shmatikov, Vitaly, "Gone In Six Characters: Short URLs Considered Harmful for Cloud Services." Blog entry dated April 14, 2016; retrieved April 26, 2016. |date=14 April 2016 |access-date=26 April 2016 |archive-url=https://web.archive.org/web/20160423121255/https://freedom-to-tinker.com/blog/vitaly/gone-in-six-characters-short-urls-considered-harmful-for-cloud-services/ |archive-date=23 April 2016 |url-status=live }}</ref><ref>{{Cite arXiv |eprint=1604.02734v1 |last1=Georgiev |first1=Martin |last2=Shmatikov |first2=Vitaly |title=Gone in Six Characters: Short URLs Considered Harmful for Cloud Services |year=2016 |class=cs.CR }}</ref>

===Additional layer of complexity===
Short URLs, although making it easier to access what might otherwise be a very long URL or user-space on an ISP server, add an additional layer of complexity to the process of retrieving web pages. Every access requires more requests (at least one more DNS lookup, though it may be cached, and one more HTTP/HTTPS request), thereby increasing latency, the time taken to access the page, and also the risk of failure, since the shortening service may become unavailable. Another operational limitation of URL shortening services is that browsers do not resend POST bodies when a redirect is encountered. This can be overcome by making the service a [[reverse proxy]], or by elaborate schemes involving cookies and buffered POST bodies, but such techniques present security and scaling challenges, and are therefore not used on [[extranets]] or Internet-scale services.{{Original research inline|date=November 2010}}

==Notable services==
<!-- Do not add to this list unless the service is notable. One good indication of notability is an existing Wikipedia article on the service. External links and non-notable entries will be removed as spam. -->

{| class="wikitable sortable"
! Site || Company || Type || Custom URL || Comment
|-
| [[bit.ly]]  || Bitly  || general public || yes ||
|-
| [[goo.gl]]  || Google || general public || {{n/a}} || Replaced by [[Firebase#Firebase Dynamic Links|FDL]] (uses Bitly<ref>{{Cite web|url=https://firebase.google.com/products/extensions/firestore-shorten-urls-bitly|title=Firebase Extensions &#124; Shorten URLs|website=Firebase|quote=Shortens URLs written to a specified Cloud Firestore collection (uses Bitly).|access-date=8 September 2020|archive-date=25 September 2020|archive-url=https://web.archive.org/web/20200925003230/https://firebase.google.com/products/extensions/firestore-shorten-urls-bitly/|url-status=live}}</ref>)
|-
| [[g.co]]    || Google || internal || {{n/a}} || Google's link service<ref>{{cite web | url=https://techcrunch.com/2011/07/18/google-buys-g-co-to-create-an-official-url-shortcut-for-google-products/ | title=Google Buys G.Co To Create An Official URL Shortcut For Google Products | author=Alexia Tsotsis | publisher=[[Tech Crunch]] | accessdate=18 July 2011 | date=18 July 2011 | archive-date=21 July 2011 | archive-url=https://web.archive.org/web/20110721081018/http://techcrunch.com/2011/07/18/google-buys-g-co-to-create-an-official-url-shortcut-for-google-products/ | url-status=live }}</ref>
|-
| [[Hootsuite|ow.ly]] || Hootsuite Media || general public || yes ||Now inside the Hootsuite dashboard
|-
| [[t.co]]    || Twitter    || internal || {{n/a}} || Twitter's link service<ref>{{Cite web |url=https://help.twitter.com/using-twitter/url-shortener |title=About Twitter's link service |access-date=20 September 2021 |archive-date=2 April 2023 |archive-url=https://web.archive.org/web/20230402162247/https://help.twitter.com/en/using-twitter/url-shortener |url-status=live }}</ref>
|-
| [[TinyURL]] || TinyURL || general public || yes ||
|-
| [[Wikipedia:URLShortener|w.wiki]] || Wikimedia Foundation || internal || {{n/a}} || Users can generate links to Wikimedia Foundation projects only.
|-
| [[youtu.be]]|| YouTube (Alphabet)  || internal || {{n/a}} || Announcement of youtu.be Links<ref>{{Cite web |url=https://blog.youtube/news-and-events/make-way-for-youtube-links/ |title=Make Way for youtu.be Links |access-date=19 September 2021 |archive-date=21 September 2021 |archive-url=https://web.archive.org/web/20210921030713/https://blog.youtube/news-and-events/make-way-for-youtube-links/ |url-status=live }}</ref>
|}

[[Open source]] and commercial scripts are also available for redirecting and shortening links, usually written in [[PHP]] as a [[web application]] or a plugin for one of the popular applications such as [[WordPress]]. Such scripts avoid many issues with shortening services, keep the domain name as part of the shortened link, and can be made private.

==See also==
{{Portal|Internet}}
<!-- Please keep entries in alphabetical order & add a short description [[WP:SEEALSO]] -->
{{div col|colwidth=20em|small=yes}}
* [[Country code top-level domain]]
* [[Domain Name System]]
* [[Emoji domain]]
* [[Generic top-level domain]]
* [[Link rot]]
* [[List of Internet top-level domains]]
* [[Semantic URL]]
* {{annotated link|Service d'adresse mondial}}
* [[Vanity domain]]
{{div col end}}
<!-- please keep entries in alphabetical order -->

==References==
{{Reflist}}

==External links==
* [http://searchengineland.com/analysis-which-url-shortening-service-should-you-use-17204 Comparison of URL Shortening Services], [[SearchEngineLand]]. April 2009.

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