Tropical calculation API

Western Astrology API for Developers

Yes—AstroAPI supports a documented Western astrology calculation workflow. Tropical zodiac output is the default, with apparent geocentric planetary positions, birth charts, equal and whole-sign houses, aspects, synastry, and natal-to-transit comparisons returned as structured JSON.

Read the birth chart docs Explore use cases

What the Western astrology API includes

AstroAPI calculates apparent geocentric ecliptic longitude for the Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Each returned body includes its selected-zodiac longitude, sign position, an apparent one-day motion value, and a retrograde flag.

Default zodiac
Tropical
Position frame
Apparent geocentric longitude
Public date window
1900-01-01 through 2050-12-31

Birth charts

Planet positions, signs, chart angles, houses, aspects, nodes, and calculation metadata.

Equal and whole-sign houses

Ascendant, Midheaven, and the selected supported house system for chart rendering.

Natal aspects

Ten documented aspect types using fixed, symmetric longitude-separation orbs.

Synastry geometry

Two complete charts and their cross-chart aspects, without compatibility scoring.

Natal-to-transit aspects

Compare a natal chart with one caller-supplied transit date and time.

Structured signals Beta

Deterministic transit fields for downstream editorial logic—not generated horoscope prose.

What can you build with it?

The endpoints are designed for server-side product backends. A client application can turn the returned data into a chart wheel, accessible table, natal report, synastry comparison, or calendar that evaluates selected transit instants.

  • Natal chart pages and saved chart profiles
  • Custom SVG or Canvas chart renderers
  • Relationship and synastry interfaces based on raw cross-aspects
  • Transit views for dates and times chosen by the caller
  • Rule-based editorial systems that preserve their own interpretive voice

See the AstroAPI use-case guide for architecture and privacy considerations before collecting birth information.

Current calculation boundaries

AstroAPI returns calculation data, not predictive certainty or professional advice. Your application owns its interpretations, editorial claims, and treatment of user data.

  • Placidus, Koch, Campanus, Regiomontanus, Porphyry, and house systems beyond equal and whole sign are not implemented
  • No progressions, solar returns, composite charts, Davison charts, or midpoint charts
  • No exact ingress/egress search, date-range event scan, or refined station time
  • No applying/separating flags, user-configurable orbs, dignity scoring, or prose interpretations
  • No topocentric positions, right ascension, declination, altitude/azimuth, or distance
  • The field labeled true node is currently identical to the documented mean-node result

Read Calculation methodology and limitations before comparing output with another ephemeris or astrology application.

Start with the documented contract

  1. Collect an explicit date, local time, IANA timezone, latitude, and longitude.
  2. Send the request from your server with an API key in the Authorization header.
  3. Validate the response and render the calculation in your own product interface.