Astro Agents vs Swiss Ephemeris vs computing it yourself
An honest comparison for financial astrology and backtesting: where a hosted, verifiable API saves you work, and where a local library is simply the better tool.
| Astro Agents API | Swiss Ephemeris | DIY (Skyfield / SPICE + JPL kernels) | |
|---|---|---|---|
| What it is | A hosted HTTP API (REST, MCP, A2A) and a Python client | A C library (with bindings) you embed | Your own code on Skyfield or NASA's SPICE, with JPL kernels |
| Ephemeris | NASA/JPL DE440 (1800-2200 served) | Its own compressed files derived from JPL ephemerides; can also read JPL files | Any JPL kernel you download (DE440, DE441...) |
| Accuracy | Within 0.024″ of JPL Horizons on 12,400 values (published benchmark) | Very high: Astrodienst documents agreement with JPL far below an arcsecond | As good as the kernel and your frame handling: the same class |
| Event calendar | Ready: ingresses, stations, lunations, eclipses with type, aspects, parallels, out-of-bounds, to the minute | Building blocks (eclipse and crossing functions); the scan and bisection are yours | Yours to write: root finding for every event kind, eclipse classification |
| Gann lines, Mean of 5, Circle of 8, price levels | Built in | Yours to write | Yours to write |
| Time zones and historical DST | Resolved for you from the place | Yours (the library takes UT/TT) | Yours |
| Proof of what you used | SHA-256 of every input and result; free /v1/verify | None built in | None built in |
| Cost | Per call (from $0.01) or prepaid packs; nothing to install | Free under AGPL-3.0, or a paid professional licence from Astrodienst for closed-source use | Free (Skyfield is MIT; JPL kernels are public) |
| Offline and volume | Needs the network; rate-limited; paid per call | Offline, unlimited, microseconds per position | Offline, unlimited |
| Best when | You want the data now, in a backtest or an agent, and want to cite it | You compute millions of positions or ship a desktop app | You want full control and have the time |
Precision is not the difference
Swiss Ephemeris, Skyfield on a JPL kernel and this API all reproduce NASA/JPL to a small fraction of an arcsecond: far below anything a chart or a backtest can see. Choosing between them is about work, licence and provenance, not about decimals. Our own measurements are public: benchmark against JPL Horizons (12,400 comparisons, 1800-2200).
What you would have to build yourself
- A scan and bisection for every event kind (ingress, station, lunation, aspect, parallel, out-of-bounds), handling retrograde loops so no crossing is missed or doubled.
- Eclipse search and classification (total, annular, hybrid, partial; lunar umbral and penumbral).
- Apparent positions in the true ecliptic and equinox of date (light-time, aberration, precession-nutation).
- Historical time zones and daylight-saving rules when inputs are local times.
- A way to show, months later, exactly which numbers a backtest used.
When to choose a library instead
If you need millions of positions a day, must run offline, or are shipping a desktop application, per-call pricing is the wrong tool: use Swiss Ephemeris (mind its AGPL or professional licence) or Skyfield. If you want a ready event calendar and Gann lines in a notebook today, with a hash you can cite, the API is the short path.
Financial astrology data API · Examples · Live catalog and prices