The latest articles on DEV Community by Master Saw (@mastersaw). https://dev.to/mastersaw https://media2.dev.to/dynamic/image/width=90,height=90,fit=cover,gravity=auto,format=auto/https:%2F%2Fdev-to-uploads.s3.amazonaws.com%2Fuploads%2Fuser%2Fprofile_image%2F3920199%2Facfce317-3f49-406a-b09f-f9039b83f512.png https://dev.to/mastersaw en Master Saw Fri, 08 May 2026 13:43:17 +0000 https://dev.to/mastersaw/building-yarrow-an-ai-i-ching-divination-saas-in-a-few-weeks-nextjs-supabase-stripe--dd9 https://dev.to/mastersaw/building-yarrow-an-ai-i-ching-divination-saas-in-a-few-weeks-nextjs-supabase-stripe--dd9 <h2> Hey 👋 </h2> <p>Just shipped <strong>Yarrow</strong> — an I Ching ("Book of Changes") divination web app that uses an LLM to write the interpretation.</p> <p><strong>Live:</strong> <a href="https://iching.lifefinetuning.com" rel="noopener noreferrer">https://iching.lifefinetuning.com</a></p> <h2> The flow </h2> <ul> <li>User types a question</li> <li>3 coins are tossed 6 times (the casting itself is <strong>pure logic</strong>, no AI)</li> <li>The resulting King Wen hexagram (1 of 64) is identified, plus any changing-line transformation</li> <li>An LLM steeped in the Wilhelm/Baynes tradition writes the reading</li> <li>Responds in whatever language you asked in (English, Chinese, etc. — handled by the model)</li> </ul> <h2> Tech stack </h2> <ul> <li> <strong>Next.js 16</strong> + Tailwind 4 + TypeScript on Vercel</li> <li> <strong>Supabase</strong> (auth + Postgres + magic-link email via Resend)</li> <li> <strong>Stripe</strong> (monthly $9.99 / annual $79)</li> <li> <strong>DeepSeek</strong> for the AI (cheap, works well for both English and Chinese)</li> <li> <strong>Resend</strong> for transactional email</li> <li> <strong>PostHog</strong> for product analytics + Session Replay</li> </ul> <h2> Things I think are interesting </h2> <ul> <li>The hexagram engine is <strong>pure logic</strong>, not AI. I encode all 64 hexagrams as binary strings and look up the King Wen number. The AI only writes the <em>interpretation</em> — it can never hallucinate a hexagram.</li> <li>Each reading gets a public shareable URL (<code>/r/[id]</code>) with its own dynamically generated OG image (your question + the hexagram visual).</li> <li>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.</li> </ul> <h2> Free tier </h2> <ul> <li>1 reading per day anonymous</li> <li>3 per day signed-in</li> <li>Unlimited on subscription</li> </ul> <h2> What I'm looking for </h2> <ul> <li>General UX feedback — is the page clear? Does it feel respectful or like fortune-cookie BS?</li> <li>I Ching practitioners — does the system prompt feel grounded or shallow?</li> <li>Other devs — anything you'd structure differently in the auth/payment/share flow?</li> </ul> <p>Solo builder in Malaysia. Happy to answer technical questions or hear honest criticism. 🙏</p> nextjs webdev indiehackers showdev