A vaguely disconcerting app from researchers at the University of Cambridge can guess how old you are, how smart you are and who you like to sleep with.

It's not magic, and it's not psychic. Instead, the recently redesigned tool, called "Apply Special Sauce," is based entirely on the pages you've "liked" on Facebook.

The app essentially works by comparing your "likes" against those of millions of other people. After you grant it access to your Facebook account, it sucks up the records of every page you've ever liked and runs that "digital footprint" against a vast internal model that Cambridge has built from tens of thousands of personality tests and 6 million social media profiles.

Based on how closely your likes do or do not adhere to that model, Apply Special Sauce can guess a lot of things about you — including your age, politics, sexual preference and level of intelligence. And while the app cautions that it's a measure of how you display your personality online, and not of your personality itself, I found that it was startlingly accurate: It got my gender, my job and my age right, within a year, and it accurately predicted my relationship status, sexual orientation and political and religious affiliations (though we won't get into those here!). When researchers at Cambridge and Stanford published a paper on their model this year, they found that it guessed personality better, sometimes way better, than real people did.

It's a good party trick, and a fun application of a technology that's grown quite trendy in recent months. But more than that, Apply Special Sauce is further proof that even the smallest, most casual signals we throw off into the digital ether don't disappear when we stop thinking about them.

Past research has already demonstrated, for instance, that these sorts of algorithms and models can accurately guess your sexuality from your Facebook likes, even if you don't like any explicitly gay or straight pages. And Facebook has shown it can guess how you'll vote based purely on your cultural tastes.

So far, none of this has probably impacted you — but that's changing, and quickly. The Apply Special Sauce app exists largely to advertise Cambridge's technology to private companies, who could use it in market research, customer service and ad targeting.

More to the point, it's only one of many such services to come to the fore lately: Crystal — a new plug-in for Gmail dubbed "psychic" and "creepy" by some users — promises to analyze the personalities of people who email you and recommend ways to communicate better; IBM's Personality Insights tool, meanwhile, will infer "cognitive and social characteristics," including psychological needs, from any texts, tweets and forum posts that you feed it.

Wheter any of these services can get your personality exactly "right," of course, is anybody's guess. But don't take my word for it: You can try Apply Special Sauce yourself at http://applymagicsauce.com/test.html.