About

HoroscopePrompt computes a chart and turns it into a prompt for an AI: a custom core does the maths on NASA/JPL ephemerides, a language model writes the interpretation.

What it does

A natal chart, an annual chart (solar return) and progressions, transits to the natal chart, relationship charts in three techniques (synastry, composite, combined chart), the quality of today and a chart of any given moment. Every technique comes with several reading variants — including an "astrology teacher" one that walks you through it and a "data only" one for writing your own prompt. The full walkthrough is in the Guide.

How it computes

A custom calculation core on NASA/JPL DE440 ephemerides, covering 15 Oct 1582 – 31 Dec 2099. Seven house systems (Placidus, Koch, Regiomontanus, Campanus, topocentric, equal, whole sign), tropical and sidereal zodiac, true and mean node, and your own aspect orbs. Where the result is uncertain — most often the birth time and historical time zones — the app says so out loud. Details in How it works.

Where it runs

Entirely in your browser. Your birth date, time and place never leave your device, nothing is sent to a server, and the prompt is anonymous by default. You can install it as an app (PWA) and use it offline. What is stored where is covered in Privacy.

Data source and licence

Ephemeris data: NASA JPL DE440 (public domain). The libraries used and the app's licence terms are on the Licenses page.

Who is behind it

The app is built and written by one person — see About the author.

Contact: