From a security standpoint, blindly clicking on redirect URLs is probably not the best idea, especially if you don't know (or don't implicitly trust) the person who shared it. In fact, even a trusted user's account could theoretically be hijacked, as happened earlier today when an XSS attack was launched against Twitter.
Thankfully, many URL shortening services offer ways of previewing the full URL before visiting it. Instructions for some of these sites follow (roughly in order of popularity). Note that I do not necessarily endorse any of the services below; this information is given for information purposes only, based on what I was able to find out by researching and testing each service.
Add "preview." before the "tinyurl.com" portion of the URL to see where the link will take you, e.g. you can change http://tinyurl.com/cz23u4 into http://preview.tinyurl.com/cz23u4
Better yet, you can force TinyURL to always take you to the preview link whenever you click on a tinyurl.com shortcut. If you go to http://tinyurl.com/preview.php you can set a cookie for the site that will enable this feature.
Bitly.com / bit.ly / j.mp / urls.im (and Bitly Enterprise sites like amzn.to, aol.it, atmlb.com, bbc.in, bhpho.to, binged.it, bloom.bg, buff.ly, cnet.co, huff.to, lat.ms, nyr.kr, nyti.ms, on.fb.me, on.mtv.com, on.vh1.com, oreil.ly, politi.co, tcrn.ch, usat.ly, wapo.st, yhoo.it, etc.)
Just add a plus ("+") after a bit.ly URL to see where the link will take you, and also to get statistics for that shortened URL (bit.ly, bitly.com, j.mp, and urls.im are interchangeable). For example, you can change http://bit.ly/2KeAT into http://bit.ly/2KeAT+ which will redirect to http://bit.ly/info/2KeAT
Alternatively, you can add "/info" after the domain portion of the URL. For example, you can change http://bit.ly/2KeAT into http://bit.ly/info/2KeAT
Note that amzn.to links always redirect to Amazon.com, and nyti.ms links redirect to nytimes.com (The New York Times). These companies have Bitly Enterprise (formerly known as "bit.ly Pro") accounts and use the special URLs to link only to their own sites, so you can be reasonably confident about where these URLs will take you. Other Bitly Enterprise sites like oreil.ly (owned by O'Reilly Media) do not link exclusively to one specific site. All Bitly Enterprise addresses, regardless of which company is responsible for them, can be previewed the same way as regular bit.ly addresses using the methods outlined above.
Google's short URLs can be previewed the same way as bit.ly URLs. Just add a plus ("+") after a goo.gl URL to see where the link will take you, and also to get statistics for that shortened URL. For example, you can change http://goo.gl/1tRbb into http://goo.gl/1tRbb+ which will redirect to http://goo.gl/info/1tRbb
Alternatively, you can add "/info" after the "goo.gl" portion of the URL. For example, you can change http://goo.gl/1tRbb into http://goo.gl/info/1tRbb
Just add a hyphen ("-") to the end of any is.gd URL to preview it, e.g. http://is.gd/rZ7U can be changed into http://is.gd/rZ7U-
Snipurl / Snipr / Snurl / Sn.im / Cl.lk
Add "peek." before the snipurl.com, snipr.com, snurl.com, sn.im, or cl.lk part of an address to find out where the link leads, e.g. http://snipurl.com/fpyfq can be changed into http://peek.snipurl.com/fpyfq
Just add a tilde ("~") to the end of any tiny.cc URL to preview it and get statistics for it, e.g. http://tiny.cc/d7bza can be changed into http://tiny.cc/d7bza~
Simply add a question mark ("?") to the end of any BudURL shortcut to preview it, e.g. you can change http://budurl.com/gtg3 into http://budurl.com/gtg3?
StumbleUpon's URL shortener, su.pr, can be previewed similarly to bit.ly; just add a "+" after a su.pr URL to get a preview page, e.g. you can change http://su.pr/2xZo8c into http://su.pr/2xZo8c+ (Note that su.pr shortcuts put an annoying StumbleUpon bar across the top of the destination page.)
This service provides a preview if you add a tilde ("~") after the URL. For example, you can change http://yi.tl/B03ImN into http://yi.tl/B03ImN~ to see the long URL. As a bonus, you'll also get to see the title of the destination page and see whether the URL is in Google's phishing or malware database.
When you visit a sURL.co.uk short URL, you will automatically get a preview of the destination address and its status on hpHosts, Malware Domain List, and PhishTank so you can instantly see whether it's a known malware or phishing scam site. The preview cannot be disabled. This is by far the most safety-focused URL shortening service, which is no surprise since it's operated by the maintainer of hpHosts.
Another service that automatically gives you a preview is cli.gs. The feature can be explicitly disabled by each user, if desired; there's a "Click here to disable previews" link on each preview page, which when clicked sets a cookie to disable previews in the future.
Tinyarro.ws / ta.gd
Tinyarro.ws is the only other URL shortener service I know of that automatically gives you a preview. Again, the preview can be disabled, if desired; there's a "Never show a URL preview again" link on each preview page, which when clicked sets a cookie to disable previews in the future.
Unfortunately, several popular services (including, as far as I can tell: t.co, twurl.nl, moourl.com, ow.ly, lnkd.in, lnk.ms, wp.me, mcaf.ee, and awe.sm) don't offer the ability to preview the original long URL before visiting it. Personally, I'm not interested in using URL shorteners that don't offer previews. It's just nice to give people the opportunity to be able to view the full URL without having to click the link first. However, if someone else sends you a shortened link from another service and you want to preview it, you may still be able to do so using a third-party site. Here are a couple of sites that let you do just that:
- Toolsvoid Unshorten URL - Works with almost any site
- LongURL Expand URL - Works with hundreds of popular sites
See also my follow-up article about a Firefox add-on that lets you preview full URLs automatically: LongURL: Preview Shortened URLs, No Clicking Required. (UPDATE: This add-on is no longer being developed and will not work with current versions of Firefox. The best alternative I've been able to find is unshorten.it for Firefox and Chrome.)
UPDATE, 3 Mar 2010: Removed defunct shortening services: poprl.com, sn.im (which has been replaced with st.im and cl.lk), and plurl.me. Also added the plus character shortcut to the bit.ly section.
UPDATE, 30 Mar 2010: Added tiny.cc and surl.co.uk.
UPDATE, 5 Apr 2010: Added j.mp and re-added sn.im.
UPDATE, 30 Nov 2010: Added goo.gl due to popular demand, plus mentioned bit.ly Pro. Also added a couple sites that can be used to find out long URLs, even when the shortening service itself doesn't offer a way to preview where a link will take you.
UPDATE, 25 Jan 2011: Added info about previewing cli.gs, urls.im, su.pr, fwd4.me, tcrn.ch, and bu.tt. Added moourl.com and Twitter's own t.co to the list of shorteners that unfortunately don't offer previews. Removed mentions of defunct tr.im and twurl.cc.
UPDATE, 31 Mar 2011: Added info about previewing binged.it, on.fb.me*, y.ahoo.it, and yhoo.it. Added lnk.ms, lnkd.in, mcaf.ee, and wp.me to the list of shorteners that unfortunately don't offer previews. *Note that on.fb.me is different from fb.me, and the latter cannot be previewed as far as I can tell. However, if you see a human-readable word or name after fb.me, this will redirect to one of Facebook's so-called "vanity URLs" for a user profile or fan page; thus fb.me/facebook will redirect to facebook.com/facebook.
UPDATE, 22 May 2012: Updated link and name for URLVoid's service (now called Unshorten URL instead of Extract URL). Added yi.tl preview instructions. Added bitly.com to the Bitly section and updated the old "bit.ly Pro" name to Bitly Enterprise. Added lots of Bitly Enterprise domains: aol.it, atmlb.com, bbc.in, bhpho.to, bloom.bg, cnet.co, huff.to, lat.ms, nyr.kr, on.mtv.com, on.vh1.com, politi.co, usat.ly, and wapo.st. Mentioned awe.sm. Removed st.im, short.ie, bu.tt, and kl.am, which all appear to be defunct. Removed mention of adjix.com, which is no longer accepting new URLs but is supposed to redirect previously created URLs "indefinitely" (it never offered a preview). Added note about the LongURL Firefox extension no longer being actively developed. Replaced link to Damon Cortesi's article on the Twitter StalkDaily Worm with an archived copy since the original site appears to be down.
UPDATE, 6 May 2013: Added buff.ly to Bitly Enterprise list. Mentioned unshorten.it extensions for Chrome and Firefox.
UPDATE, 10 May 2013: Updated URLVoid unshortener link to new Toolsvoid URL.
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