URL shortening

A friendly URL may be desired for messaging technologies that limit the number of 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.

So, although disguising of the underlying address may be desired for legitimate business or personal reasons, it is open to abuse.

Many web developers pass descriptive attributes in the URL to represent data hierarchies, command structures, transaction paths or session information.

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.

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.

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 – for example, Twitter with t.co,[3] Telegram with t.me, Google with g.co,[4] and GoDaddy with x.co.

Not all URI schemes are capable of being shortened as of 2011, although URI schemes such as http, https, ftp, ftps, mailto, mms, rtmp, rtmpt, ed2k, pop, imap, nntp, news, ldap, gopher, dict and dns are being addressed by such services as URL shorteners.

Typically, data: and javascript: URLs are not supported for security reasons (to combat attacks like cross-site scripting and session hijacking).

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.

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.

As a result, many have been removed from online registries or shut down by web hosts or internet service providers.

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

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

It is a legitimate concern that many existing URL shortening services may not have a sustainable business model in the long term.

[15] Shortened internet links typically use 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.

Answers blocks postings that contain TinyURLs,[citation needed] and Wikipedia does not accept links by any URL shortening services in its articles.

TinyURL countered this problem by offering an option to view a link's destination before using a shortened URL.

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.

Another operational limitation of URL shortening services is that browsers do not resend POST bodies when a redirect is encountered.