Google’s URL shortener Goo.gl was introduced last December as a part of Google toolbar and Feedburner and there wasn’t a direct way to shorten URLs via this service, like the Facebook’s URL shortener fb.me. Goo.gl was then integrated for most of the popular services from Google including Picasa, Blogger, Maps etc. A few days ago, Google opened the URL shortener for everyone, i.e. you can open up Goo.gl on your browser and shorten any URL on the fly. But Goo.gl accepts links previously shortened through other URL shorteners as well which is uncommon among other URL shortening websites. Like if you take a link shortened via bit.ly and insert it into the shortening field of Goo.gl, it still accepts it, unlike other URL shortening services which mark such practices as spamming.
If you take a URL shortened via bit.ly and use is.gd to shrink it, you are flatly denied. You’ll get a message saying that is.gd doesn’t accept URLs already shortened via other URL shortening service. On the other hand, if you insert a short URL from is.gd into bit.ly, the latter does its job all good. But when you try to open the link, bit.ly shows a warning page saying that this could be a spam attempt. Similarly other URL shorteners also don’t approve of this. But surprisingly, Goo.gl still permits shortening such URLs. What’s even more interesting is that even the other URL shorteners don’t display a spam attempt message when you input a shrunken URL from Goo.gl. So, maybe the popular URL shorteners should acknowledge Goo.gl as a standalone URL shortener and update their database and vice versa.