Sometimes, you know you’re stoned. But other times, especially if you haven’t consumed that much cannabis, it’s a little murkier. With dosages varying widely among products and the effects of cannabis equally wide-ranging, it can sometimes be difficult to judge exactly how impaired you are.

But an up-and-coming app out of the University of Chicago, called “Am I Stoned?” aims to solve the mystery for you, or, more importantly, for anyone who needs to judge your level of sobriety.

The app is still a prototype, but it’s had promising results in tests so far. It works by putting consumers through a series of tests measuring cognitive ability, reaction time, and memory, compared to their baseline.

In their controlled, double-blind study, participants took a pill containing either 0, 7.5 or 15 milligrams of THC, the psychoactive component of cannabis. They were then asked to complete tests on both a computer and an iPhone.

One involved tapping a bunch of dots in succession with your non-dominant hand, and another involved shaking your phone when a dot appeared on the screen.

Researchers found that in three of the four computer tasks, and one of the four phone tasks, people who had taken the pills with more THC had more trouble with the tasks.

They also learned that the participants were pretty good judges of how impaired they were.

As marijuana becomes more legal and commonplace, a test like this could take the place of a breathalyzer for alcohol, used for law enforcement and other officials.

The app has government funding for that reason, and the creators hope to work out all the kinks in time for summer.