If you think you look young for your age, you may want to double-check that with Microsoft’s new how-old.net, which uses the power of its Azure services to analyze your face.

The site was unveiled Thursday at the company’s Build 2015 conference to show off the powerful of its cloud service platform. The website lets you upload a photo, and then quickly analyzes the individual, and spits out an estimated age.

It can be unnervingly accurate at times—as well as unnervingly IN-accurate. We tested it using staff photos and found that a different photo of the same person, taken within the same year, could yield a different age, possibly due to lighting or facial expression.

We also tried celebrities—though one can’t always guess how old they are, whether because of work done or because it’s someone like Abe Vigoda, who many believe has looked 77 since he was a baby. Judging from the tie, this photo was probably taken in the mid-70s, when Vigoda was actually in his mid-50s.

Even the power of cloud computing can’t correctly tell how old Abe Vigoda is in his picture.

Microsoft made the site as a demo for its Azure services and said it took a couple of developers just a day to put together the entire site. It uses face detection routines from the company’s Project Oxford, which has the ability to recognize a face, guess how old the person is, and also guess the gender. 

Why this matters: Well, let’s be honest, this is just a silly way to show off some cloud services, but it’s entertaining. However, anyone who’s trying to decide which photo to put up on on their profile page, be it LinkedIn, Twitter or Tinder, and doesn’t trust the judgement of their friends could run the pic through this site to make sure they’re putting their best age forward.