Swiss Ephemeris API

Swiss Ephemeris is the de-facto standard for astronomical calculation in astrology: Astrodienst (astro.com), Solar Fire, Kerykeion and most serious software are built on it. It reads NASA JPL’s DE431 ephemeris and delivers sub-arcsecond accuracy. AstroWay API gives you direct HTTP access to it — no C library to compile, no .se1 files to download, no memory management. One POST request, JSON back.

Why Swiss Ephemeris over an API

Self-hosting Swiss Ephemeris means: build the C library (or a WASM bundle), host a few hundred megabytes of .se1 files, keep them current, and implement house cusps, aspects and phases yourself. Over an API all of that is someone else’s problem:

• Zero infrastructure — no binaries, no ephemeris files, no cold starts. Calculation runs server-side on the same engine Astrodienst uses.
• Sub-arcsecond accuracy — < 0.1″ against Astrodienst’s reference swetest CGI, verified on 818 frozen snapshot tests on every deploy.
• Full date range — DE431 covers 13201 BCE – 17191 CE, so historical and far-future charts compute without precision loss.
• More than positions — on top of the ephemeris you immediately get house cusps (15 systems), aspects, eclipses, transits and progressions — the parts you’d have to write yourself when self-hosting.

Tip

Engine accuracy is triangulated against three independent sources (swetest CGI, Kerykeion, Prokerala) plus the NASA 5-Millennium Eclipse Catalog. Numbers and method on the Accuracy page.

What runs on Swiss Ephemeris

Endpoint	Credits	Returns
/v1/chart	20	Full chart: planets + houses + aspects
/v1/planets	10	Geocentric planet positions (longitude, latitude, speed, retrograde)
/v1/houses	10	House cusps — 15 systems (Placidus, Koch, Whole Sign, Equal…)
/v1/transits	50	Transits to a natal chart for a given date
/v1/progressions	50	Secondary progressions (day = year)
/v1/eclipses	20	Solar & lunar eclipses (verified vs NASA Catalog)
/v1/moon-phase	10	Moon phase, illumination, next quarters
/v1/fixed-stars	20	Planet conjunctions with fixed stars

This is part of 714 platform endpoints — full list in the API reference.

Example

cURL

curl -X POST https://api.astroway.info/v1/planets \
  -H "X-Api-Key: aw_live_your_key_here" \
  -H "Content-Type: application/json" \
  -d '{
    "date": "1990-07-14",
    "time": "14:30:00",
    "timezoneOffset": 3,
    "latitude": 50.4501,
    "longitude": 30.5234
  }'

Node.js

const r = await fetch('https://api.astroway.info/v1/planets', {
  method: 'POST',
  headers: {
    'X-Api-Key': process.env.ASTROWAY_API_KEY!,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    date: '1990-07-14',
    time: '14:30:00',
    timezoneOffset: 3,
    latitude: 50.4501,
    longitude: 30.5234,
  }),
});
const { data } = await r.json();
console.log(`Sun: ${data.planets.sun.sign} ${data.planets.sun.degree.toFixed(4)}°`);

Python

import os, requests

r = requests.post(
    'https://api.astroway.info/v1/planets',
    headers={'X-Api-Key': os.environ['ASTROWAY_API_KEY'], 'Content-Type': 'application/json'},
    json={
        'date': '1990-07-14',
        'time': '14:30:00',
        'timezoneOffset': 3,
        'latitude': 50.4501,
        'longitude': 30.5234,
    },
)
data = r.json()['data']
print(f"Sun: {data['planets']['sun']['sign']} {data['planets']['sun']['degree']:.4f}°")

Who uses it

• Astrology-app developers — sub-arcsecond positions without self-hosting the C library
• AI agents — accurate ephemeris as grounding for LLMs (via the MCP server)
• Researchers — bulk calculation across the full DE431 historical range
• Migrating off self-host — drop-in replacement for a local swisseph build over HTTP, same precision

Pricing

Planet positions (/v1/planets) — 10 credits, full chart (/v1/chart) — 20. The Free tier (714+ endpoints, 10,000 credits/mo) covers roughly 1,000 planet requests a month, no card required.

Accuracy → Triangulation, NASA validation, snapshot tests

Quick start First request in 5 minutes

Pricing From free to Enterprise