Hey 👋
Just shipped Yarrow — an I Ching ("Book of Changes") divination web app that uses an LLM to write the interpretation.
Live: https://iching.lifefinetuning.com
The flow
- User types a question
- 3 coins are tossed 6 times (the casting itself is pure logic, no AI)
- The resulting King Wen hexagram (1 of 64) is identified, plus any changing-line transformation
- An LLM steeped in the Wilhelm/Baynes tradition writes the reading
- Responds in whatever language you asked in (English, Chinese, etc. — handled by the model)
Tech stack
- Next.js 16 + Tailwind 4 + TypeScript on Vercel
- Supabase (auth + Postgres + magic-link email via Resend)
- Stripe (monthly $9.99 / annual $79)
- DeepSeek for the AI (cheap, works well for both English and Chinese)
- Resend for transactional email
- PostHog for product analytics + Session Replay
Things I think are interesting
- The hexagram engine is pure logic, not AI. I encode all 64 hexagrams as binary strings and look up the King Wen number. The AI only writes the interpretation — it can never hallucinate a hexagram.
- Each reading gets a public shareable URL (
/r/[id]) with its own dynamically generated OG image (your question + the hexagram visual). - Anti-abuse: anonymous quota uses an IP+UA hash (not a cookie), so clearing cookies doesn't reset it. Reading slots are reserved BEFORE the AI call so people can't disconnect mid-stream to skip the count.
Free tier
- 1 reading per day anonymous
- 3 per day signed-in
- Unlimited on subscription
What I'm looking for
- General UX feedback — is the page clear? Does it feel respectful or like fortune-cookie BS?
- I Ching practitioners — does the system prompt feel grounded or shallow?
- Other devs — anything you'd structure differently in the auth/payment/share flow?
Solo builder in Malaysia. Happy to answer technical questions or hear honest criticism. 🙏