URL shortening is a technique on the World Wide Web in which the Uniform Resource Locator (URL) can be made shorter and still shorter. This is achieved by using a redirect which links to the web page that has a long URL. For example, the URL ” http://example.com/assets/category_B/subcategory_C/Foo/ ” can be shortened to ” https://example.com/Foo “, and the URL ” http://example.com /about/index.html “can be shortened to” https://goo.gl/aO3Ssc “. Often the redirect domain name is shorter than the original one. A friendly URLMay be Desired for messaging technologies That limit the number of characters in a post (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. 
Other uses of URL are “beautify” to link, track clicks, or disguise the underlying address. Although it may be desirable for business or personal reasons, it is open to abuse.  Some of the shortening service providers have found themselves on spam blacklists, because of the use of their own services. Some websites prevent short, redirected URLs from being posted.
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, the latter often requiring that the 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 – however, it is not necessary to use a specific 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 goo.gl , tinyurl.com , and bit.lycan generate URLs that are human-readable, resulting in a length-optimized service. Lastly, URL provides information on the clicks to a link receiving, which can be made easier than setting up a powerful server-side analytics engine, and does not require any access to the server.
URLs encoded in two-dimensional barcodes such as QR code are often shortened by a URL, or they may be used to reduce the number of times they are scanned.
Registering a short URL
Some websites create 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 shortening service URL; to do it in batch or on request may require the use of an API.
A few well-known websites have their own URL for their own use – for example, Twitter with t.co, and Google with goo.gl.
In URL shortening, every long URL is associated with a unique key , which is the part after its top-level domain name . For example, http://tinyurl.com/m3q2xt has a key of m3q2xt . Not all redirection is treated the redirection instruction sent to a browser can contain in their header the HTTP status 301 (permanent redirect), 302, or 307 (temporary redirect).
There are several techniques to implement a shortening URL. Keys can be generated in basic 36 , assuming 26 letters and 10 numbers. In this case, each character in the sequence will be 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 a key, a hash function can be made, or a random number generated that key sequence is not predictable. Or users may offer their own keys. For example, http://example.com/product?ref=01652&type=shirt can be shortened to http://tinyurl.com/exampleshirt .
Makers of URL shorteners usually register domain names with less popular or esoteric Top-level domains in order to accomplish achieve a short URL and a catchy name, Often using domain hack . This article is not available in English, but it is hereby incorporated by reference. Top-level domains 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 cultural or political aspects of the country in support of the top-level domain May Become an Issue for users and owners,  goal this is not usually the case.
Tinyarro.ws , and qoiob.com use Unicode characters to accomplish achieve the shortest URL possible, since more condensed URLs are possible, with a number of characters Given Compared To Those using standard has Latin alphabet . [ quote needed ]
Services may record inbound statistics, which may be viewed publicly by others. 
Expiry and time limited services
Many providers of shortened URLs claim that they will “never expire” (ie, it is always possible to use this service ) “- and remain in business ).
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 falling or even extant destination. Sometimes a short URL is useful to give someone a conversation or a couple of minutes.
Some shorteners offer a time-limited service, which will expire after a specified period. Services available include an ordinary, easy-to-say word as the URL with a lifetime from 5 minutes to 24 hours, creation of a URL which will expire on a specified date or after a specified period, creation of a very-short- lived URL of only 5 characters for typing into a smartphone , restriction by the creator of the total number of uses of the URL, and password protection. Microsoft Security Brief recommends the creation of short-lived URLs, but for reasons of convenience rather than convenience. 
An early reference is US Patent 6957224 , which describes
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 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. 
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.  The first notable URL shortening service TinyURL , Was lancé in 2002. Its popularity Influenced the establishment of at least 100 similar websites,  ALTHOUGH MOST are simply alternative domain. INITIALLY Twitter automatically translated URLs along than twenty-six characters using TinyURL, bit.ly ALTHOUGH It Began using INSTEAD in 2009  and later Developed icts own URL shortening service t.co.
On August 14th, 2009 WordPress announced the wp.me URL shortener for use when referring to any WordPress.com blog post.  In November 2009, shortened links on bit.ly were accessed 2.1 billion times.  Around that time, bit.ly and TinyURL were the most widely used URL-shortening services. 
One service tr.im, stopped short URLs Generating in 2009, blaming a revenue-generating Lack of 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.  It resumed for a time,  then closed.
The shortest possible long-term URLs were generated by NanoURL from December 2009 until about 2011, associated with the top-level .to (Tonga) domain, in the form http://to./xxxx , where xxxx represents a sequence of random numbers and letters. 
On December 14, 2009 Google announced a service called Google URL Shortener at goo.gl, which originally was only available for Google products (such as Google Toolbar and FeedBurner )  and extensions for Google Chrome .  On 21 December 2009, Google has Introduced YouTube URL Shortener, youtu.be.  From September 2010 Google URL Shortener becomes available via a direct interface. The goo.gl provides a QR code generator. [ quote needed ]
The main advantage of a short link is that it is, in fact, short, and can be easily answered. May easily be discovered; this may be advantageous, disadvantageous, irrelevant gold. A short link which expires, or can be terminated, has some security advantages.
This article’s Criticism or Controversy section may have compromised the article’s neutral point of view of the subject . Please integrate the section into the article as a whole, or rewrite the material. (October 2011)
Short URLs often circumvent the intended use of top-level domains for the country of origin; Domain registration in many countries requires proof of physical presence.
URL shortening may be used by 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” and “safe”. 
In addition, “u.nu” made the following announcement on closing operations:
The last straw came on September 3, 2010, when the server was published in the United States. The disconnection of the server causes serious problems, and to be honest, the level and the 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. 
Google’s url-shortener discussion group has frequently included messages that have been reported as spam. 
A study in May 2012 showed that 61% of URL shorteners had shut down (614 of 1002).  The most common cause has been abused by spammers.
The convenience offered by the shortening also introduces potential problems, which have led to criticism of the use of these services. Short URLs, for example, will be subject to link to 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.  In late 2009, the Internet Archive started the “301 Works” projects,  together with twenty collaborating companies (initially), whose short URLs will be preserved by the project. The URL shortening service provides a complete set of links to its website, so it can also provide links to other websites. A circumvention could be that of a third party service – it is not common.
Shortened internet links typically, and are therefore under the jurisdiction of that nation. Libya , for instance, exercising its control over the .ly domain in October 2010 to shut down vb.ly for violating Libyan pornography laws. Failure to predict such problems may result in a lack of due diligence . 
Blocking and banning
Some websites prevent short, redirected URLs from being posted.
In April 2009, TinyURL was reported in Saudi Arabia .  Yahoo! Answers blocks postings that contain TinyURLs, [ citation needed ] and Wikipedia does not accept links by any URL.  The Reddit Community strongly discourages – and in some subreddits, outright banners – URL shortening services for link submissions, because they say the origin of the domain name and whether or not the link has been submitted to Reddit to use link shorteners for Reddit link submissions. 
Sites such as Adf.ly use a number of advertising techniques, including interstitial advertising , to generate revenue. This may deter readers.
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 , redirecting to shock sites , or affiliate websites. The short URL can allow blacklisted URLs to be accessed, bypassing site blocks; this facilitates redirection of a user to blacklisted scam pages or pages containing malware or XSS attacks. TinyURL tries to disable spam-related links from redirecting.  ZoneAlarm , however, has warned its users: ” TinyURL may be unsafe.“TinyURL countered this problem by providing an option to view a link to a destination before using a shortened URL.  To destination preview may also be obtained. prefixing the word “preview” to the URLs TinyURL, for example, the destination of http://tinyurl.com/8kmfp is Revealed by Reviews entering http://preview.tinyurl.com/8kmfp Other URL shortening services Provide a similar destination. display.  Security professionals suggest users check That was short URL’s destination before Accessing it [ citation needed ], following an instance where shortening service cli.gs was compromised, exposing millions of users to security uncertainties.  There are several web applications that can display the URL destination of a shortened URL. [ quote needed ]
Some URL shortening services filter their links through bad-site screening services like this Google Safe Browsing . Many sites that accept user-submitted content block links, however, to certain domains, are known to us, and are known to us.
Another privacy problem is that many services’ shortened URL is small enough that it is vulnerable to brute-force search. <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> Google cancer and mental diseases), addiction treatment centers, abortion providers, correctional and juvenile detention facilities, payday and car-title lenders, gentlemen’s clubs, etc. ”  
Additional layer of complexity
Short URLs, where is it possible to access the 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 aussi the risk of failure, since the shortening service may become unavailable. Another operational limitation of URLs is that browsers do not resend POST bodies when a redirect is encountered. This can be overcome by making the service a reverse proxyConstructing schemes and strategies for implementing security and scaling challenges, and they are therefore not used on extranets or Internet-scale services. [ original research? ]
- bit.ly (Bitly)
- goo.gl ( Google )
- is.gd (Is Good)
- ow.ly (Hootsuite)
- t.co (Twitter)
- TinyURL (Gilby)
- youtu.be (YouTube)
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, and can be made private.
- Country code top-level domain
- Domain name system
- Generic top-level domain
- Link rot
- List of Internet top-level domains
- Semantic URL
- Vanity domain
- Vanity URL
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