I'm the developer of Constella. I've been working on it for about a year.
ANSWER — what it does
Western astrology apps are everywhere. Saju, the Korean four pillars system
(bazi in Chinese), barely exists in English. Where it does, it's usually a thin
wrapper that takes your birthday and hands back a paragraph.
Saju works differently from a sun sign. It takes your birth date AND time,
converts it to the lunisolar calendar, and produces four pillars — year, month,
day, hour — each one a pair of heavenly stem and earthly branch. From those
eight characters you read the balance of five elements: wood, fire, earth,
metal, water. What you have too much of, what you're short on, and which
element the tradition says would bring you back into balance. That last one is
called yongshin, and it's the part English-language apps skip entirely.
Constella computes all of that on your device and reads it back in English.
Around it there's a daily card drawn against the day's pillar, eight life
domains, compatibility between two charts, and longer life and yearly readings.
Tarot, live planetary positions and a 16-type personality test share the same
card interface.
BETTER — versus the alternatives
Co-Star and The Pattern: a different system entirely. Those read western natal
charts. This reads the East Asian four pillars, which needs your birth hour and
produces an element balance rather than planet-in-sign statements.
The LLM fortune apps: there is no model in here. Readings come out of a rule
engine — a separate Swift package, roughly 1,400 lines — that resolves stem and
branch combinations into text slots. The same birth data always returns the same
reading, and it works with the network switched off. An LLM would have been far
easier to build and would invent a different answer every time you asked.
The free bazi calculators: those hand you a raw chart in jargon. The actual work
here was turning that chart into something readable without flattening it into a
horoscope blurb.
Calculation is local. Only the optional Bond Search feature shares chart data,
through CloudKit.
COST
Free, no ads.
Optional in-app purchases — consumable star tickets that unlock deeper
readings: 0.99, 2.99, 9.99, 19.99 USD. Tickets never expire.
Optional card deck themes: 2.99 USD each.
No subscription. Nothing is rented.
App Store: https://apps.apple.com/us/app/id6769477419
Languages: English, Korean, Japanese, Simplified Chinese, Traditional Chinese.
Who I am: James Song, Pentarab — [info@pentarab.com](mailto:info@pentarab.com)
Privacy policy: https://pentarab.com/constella/privacy
Terms of service: https://pentarab.com/constella/terms
Happy to answer anything about how the chart calculation works, or about saju
itself if you've never come across it. Having your saju read is an ordinary
thing in Korea — before a wedding, a job change, naming a baby — and it was
strange to find so little of it in English.
https://i.redd.it/t76dwuyaduoh1.png
Source: r/iosapps · by /u/robostoa