The Seer · PWA overview
Most astrology apps split into two camps. Serious tools with ugly interfaces, or pretty apps delivering generic sun-sign horoscopes. I wanted a third option: a mobile-first app that gets the calculations right and speaks under the template of proper data.
The constraint that decided the shape of the product: the astronomical calculations had to run in the browser, not on a server. Swiss Ephemeris has powered desktop astrology software for three decades. Compiling it to WebAssembly put that precision directly on the client. No round trips, no paywalled API, no approximation.
The Seer is a bilingual PWA with four product surfaces: an Oracle for question-led readings, a Cosmos Dashboard for daily forecasts, a Natal Chart with AI personality synthesis, and Bonds for two-person synastry. Installable on iOS and Android. English and Japanese languages available.
Oracle · Reading view
Cosmos · Ephemeris view
Bonds · Relational readings
Real astronomy in the browser
Swiss Ephemeris compiled to WebAssembly runs client-side. The chart you see is the chart the sky actually had. Real positions, real aspects, real houses, calculated locally. No API dependency, no server cost per reading.
The oracle is a typed pipeline, not a freestyle LLM
Every question gets classified by domain, scored against the transits actually relevant to that domain in your chart, and capped at four sentences. The LLM responds from real astronomical context, not improv. A "Why did The Seer say this?" panel exposes the underlying astrology behind every reading.
Crisis-aware by default
Astrology readings get asked the hardest questions people are sitting with. The Seer detects self-harm language and surfaces crisis-hotline numbers before any oracle response.
Frontend. React 18, TypeScript, Vite.
Astronomy. Swiss Ephemeris compiled to WebAssembly, running client-side.
AI. GPT-4o-mini with a custom oracle-voice prompt. Transit context injected into every reading.
Infrastructure. Cloudflare Pages, D1, serverless functions.
Observability. PostHog for product analytics, Sentry for errors.
Delivery. Installable PWA, offline core assets, iOS and Android.
Live at theseer.xyz in private testing with a small circle. This is a craft project.
theseer.xyz GitHubThe hardest part was building something that did not exist yet. Other astrology apps, Co-Star for example, give daily readings and stop there. I wanted to go past that, and there were no samples to reference. The other hard part was directing the LLM properly so it never replied with anything harmful or negative. That took real iteration.