Accurate, open-source astrology calculations. Free forever.
I looked for a reliable, open astrology calculation library and couldn't find one that was accurate, well-documented, and free without strings attached. So I built it.
Jzero is my way of giving that back. If you're building an astrology app, learning astronomical math, or just curious — this is yours to use, modify, and share.
No paywalls. No licenses to negotiate. Just the math, done right.
Jzero calculates birth charts, transits, synastry, and house cusps using Swiss Ephemeris — the same engine professional astrology software relies on. It's accurate to ±0.0001°.
You can use it as a JavaScript library, as an HTTP API from any language, or fork it and port it to whatever stack you're working in. It's MIT licensed. Do what you want with it.
git clone https://github.com/The-Decans-Project/Jzero.git
cd Jzero
npm install
node examples/basic-birth-chart.jsFull documentation in QUICKSTART.md. API docs in SERVER_API.md.
The codebase is modular and well-documented. Core calculations are separated from higher-level techniques, so it's easy to understand, extend, or contribute to.
- ARCHITECTURE.md — how it's structured
- CONTRIBUTING.md — how to get involved
- examples/ — working code to get you started
If you find a bug, open an issue. If you want to add something, open a PR. All skill levels welcome.
MIT. Commercial use is fine — just be aware that Swiss Ephemeris has its own license for commercial deployments.
This is a personal project, built and maintained in my own time. If it helps you build something, a coffee goes a long way.
