Co-Star Astrology App: How It Works, Why Its Horoscopes Wreck Us

We bow to the goddess of brutally honest push notifications. 

A blue zodiac wheel on the outer walls of an old building
Unsplash / Josh Rangel

It did not take the Co-Star Astrology App very long to issue its first withering burn. “Correct all the time-wasting at your job,” read the notification hovering over my Twitter feed at noon on a Wednesday.

“Be quiet,” I hissed. It was my first day using Co-Star, the cultish astrology app whose brutal notifications have become a cultural meme, and already, I was being read by the A.I. equivalent of a nosy aunt giving me demonstrative looks of concern over a large glass of wine.

Co-Star has exploded in popularity since its debut a year and a half ago, racking up tens of thousands of positive reviews in the Apple Store and nearly three million downloads. In an announcement on April 16, the Co-Star team, anchored by Banu Guler, Ben Weitzman and Anna Kopp, announced they’d hit a $5 million funding mark with investors, allowing them to finally build out an Android app to accompany their already-successful iOS version.

“By positioning human experience against a backdrop of a vast universe, Co–Star creates a shortcut to real talk in a sea of small talk: a way to talk about who we are and how we relate to each other,” read the announcement tweet. “It doesn’t reduce complexity. It doesn’t judge. It understands.”

Photo evidence of this reporter being chastised by Co-Star. 

Maddy Foley 

We might consider Co-Star’s ascent as the beginning of “Big Zodiac,” a phenomenon ushered in by the millennial proclivity for self-care and witchy aesthetics. But the Co-Star astrology app also tries to stand out in a growing pool of astro-tech products as a platform that combines seemingly “hard” science — they self-describe as “A.I.-powered” and claim to use “NASA data” — with unsettlingly specific astrology readings. The horoscopes are so spot on in some cases, users have even questioned whether their data is somehow being accessed. After all, how else would the great goddess of brutally honest push notifications know to shame me the second my eyes wandered over to Twitter?

How Co-Star Works

As is common within the astrology world, new Co-Star users are prompted to provide their date of birth, along with the time and location. Co-Star accesses data from NASA to pinpoint the positioning of the stars and planets in the sky at the moment you entered into the world. From there, a natal chart, a classic tool of astrology, is generated. Co-Star doesn’t just consider your sun sign — the zodiac sign determined by your date of birth, the one you almost certainly answer with when asked, “What’s your sign?” — but takes into account your entire astrological profile.

That information is then fed into an A.I. algorithm, which spits out “day at a glance” notifications, along with a list of your current “problem areas.”

It’s this balance, of almost laughably blunt — but accurate — astrological advice, that has gained Co-Star such a fervent following, especially among millennial women. The accuracy is often unsettling. While following up on email requests for an interview with Co-Stars’ founders, this reporter got a reminder to “send them a note.”

Erin Clancy, a graduate student in Kentucky, told Inverse that it’s this unique combination which allows Co-Star to provider her with what she says is genuine emotional guidance.

“Its push notifications act as daily affirmations for me,” says Clancy.

Alex Crump, who works in advertising in Cleveland, Ohio, began using Co-Star on the advice of a friend (the more you talk to people about Co-Star, the more you realize that everyone heard about the app from a sister or a cousin or a friend). Her response to my initial question, “Does Co-Star wreck you?” was simply, “It does.”

But in contrast to the abundance of self-effacing Co-Star related posts, Crump says she never feels that her “Day at a glance” notifications are brutal, or mean. They’re just pertinent to her life. Whether their scientific base is actually science or just self-fulfilling magic, Crump says that on at least one occasion, she took Co-Star’s advice to “take a risk today” when she was on the fence about a life decision.

Sure, they may “hurt so good,” but they’re also empowering, says Crump.

Banu Galer, co-founder and CEO of Co-Star, has denied that Co-Star accesses additional information. But go through Co-Star’s user policy, and you’ll note that the app uses cookies to note your device type, the frequency with which you check the app and whether you were referred through another platform, like Instagram.

Co-Star’s Other Secret Ingredient: Sass

While the substance of Co-Star’s horoscopes are determined by the stars, their style results from human input. Each eerie push notification stems from an A.I. algorithm that’s in fact powered by a group of freelance writers and astrologers, who work to distill the planetary data into succinct phrases that, Galer has said, mimic how friends talk to one another.

After all, friends don’t tell friends, “The moon is currently three houses away from where Neptune was when you were born” (something that is, apparently, happening to this Libra writer). But friends might tell friends, “You seem stressed, and that stress seems like it’s filling you with regret, or maybe confusion.” And they have said that, or at least, a variation of that. And yes, when Co-Star said as much, I groaned at the accuracy.

Cynthia Betubiza, a graduate student in New York, joined Co-Star after joking with her cousin about their respective signs. But she’s become a huge fan of the platform, often finding her notifications “uplifting without being sappy.” Betubiza thinks Co-Star’s popularity has grown on the back of cultural upheaval. The few studies on astrology seekers, like this one from 1982, have found that people turn to the sky, to the planets and the stars, when faced with stressors in their lives.

It makes sense, then, that astrology has become a touchstone for younger generations who have grown up amid long-running wars, climate change and threats of nuclear disaster: “I think in all of us there’s a spirituality void that we find a way to fill with something,” Betubiza said.

And for millennials, that something might just be advice from the stars.