How to Build an Astrology API from Scratch

Why Build Your Own Astrology API?

Most developers searching for a "Swiss Ephemeris API" really want one thing: a hosted endpoint where they send a date, time, latitude and longitude and get back accurate planetary positions, the ascendant, and a full birth chart as JSON. Building that yourself requires deep knowledge of astronomical calculations, ayanamsa systems, house math, and API architecture — typically 6-12 months of work.

There is a faster, more transparent path. Vedika runs on the XALEN Ephemeris — our own astronomical engine, which we open-sourced under Apache-2.0 (published on crates.io, PyPI as xalen, and npm as @xalen/wasm, with 2,200+ tests). Unlike most astrology APIs that resell a third-party closed ephemeris, XALEN is independently auditable: it is validated against reference ephemerides including JPL DE440 and the industry-standard swetest tool, with sub-arcsecond agreement and zero charts deviating beyond 0.1° across a 5-million-chart validation. You can read the math, or skip the build and call it directly.

Core Components

An astrology API requires these fundamental components:

• Ephemeris Engine - XALEN Ephemeris (open-source, Apache-2.0) for planetary positions
• Timezone Database - Historical timezone conversions
• Ayanamsa Calculator - Sidereal zodiac corrections
• House System Calculator - Multiple house systems
• Aspect Calculator - Planetary relationships
• Yoga Detector - Vedic planetary combinations

Step 1: Ephemeris Setup

A high-precision ephemeris library is the foundation of any astrology API:

// Node.js with an ephemeris library (e.g. native bindings)
const ephemeris = require('your-ephemeris-lib');

// Initialize ephemeris data path
ephemeris.setEphePath('./ephe');

// Calculate planetary position
function getPlanetPosition(julianDay, planet) {
    const result = ephemeris.calcUt(
        julianDay,
        planet,
        ephemeris.FLAGS.SIDEREAL | ephemeris.FLAGS.SPEED
    );

    return {
        longitude: result.longitude,
        latitude: result.latitude,
        distance: result.distance,
        speedLong: result.longitudeSpeed
    };
}

Step 2: Julian Day Conversion

All astronomical calculations use Julian Day numbers:

function dateToJulianDay(date, time, timezone) {
    // Convert local time to UTC
    const utcDate = convertToUTC(date, time, timezone);

    // Calculate Julian Day
    const jd = ephemeris.julday(
        utcDate.year,
        utcDate.month,
        utcDate.day,
        utcDate.hour + utcDate.minute / 60,
        ephemeris.GREG_CAL
    );

    return jd;
}

Step 3: API Endpoint Design

RESTful endpoint structure for astrology APIs:

// Express.js API routes
const express = require('express');
const router = express.Router();

// Birth Chart endpoint
router.post('/v2/astrology/birth-chart', async (req, res) => {
    const { datetime, latitude, longitude, ayanamsa } = req.body;

    // Validate inputs
    if (!datetime || !latitude || !longitude) {
        return res.status(400).json({ error: 'Missing required fields' });
    }

    // Calculate chart
    const chart = await calculateBirthChart({
        datetime,
        latitude,
        longitude,
        ayanamsa: ayanamsa || 'lahiri'
    });

    return res.json(chart);
});

// Panchang endpoint
router.get('/v2/astrology/panchang', async (req, res) => {
    const { date, latitude, longitude } = req.query;
    const panchang = await calculatePanchang(date, latitude, longitude);
    return res.json(panchang);
});

Step 4: Ayanamsa Implementation

Supporting multiple ayanamsa systems:

const AYANAMSA_CODES = {
    'lahiri': ephemeris.SIDM.LAHIRI,
    'raman': ephemeris.SIDM.RAMAN,
    'krishnamurti': ephemeris.SIDM.KRISHNAMURTI,
    'fagan_bradley': ephemeris.SIDM.FAGAN_BRADLEY,
    'true_chitra': ephemeris.SIDM.TRUE_CITRA
};

function setAyanamsa(ayanamsa) {
    const code = AYANAMSA_CODES[ayanamsa] || ephemeris.SIDM.LAHIRI;
    ephemeris.setSidMode(code, 0, 0);
}

function getAyanamsaValue(julianDay, ayanamsa) {
    setAyanamsa(ayanamsa);
    return ephemeris.getAyanamsaUt(julianDay);
}

Step 5: House Calculation

function calculateHouses(julianDay, latitude, longitude, houseSystem) {
    const houses = ephemeris.houses(
        julianDay,
        latitude,
        longitude,
        houseSystem // 'P' for Placidus, 'W' for Whole Sign, etc.
    );

    return {
        ascendant: houses.ascendant,
        midheaven: houses.mc,
        cusps: houses.house // Array of 12 house cusps
    };
}

Why Use Vedika API Instead?

Building from scratch is educational but impractical for production:

Quick Integration with Vedika

// Instead of building from scratch, use Vedika API
const response = await fetch('https://api.vedika.io/v2/astrology/birth-chart', {
    method: 'POST',
    headers: {
        'Content-Type': 'application/json',
        'Authorization': 'Bearer YOUR_API_KEY'
    },
    body: JSON.stringify({
        datetime: '1990-05-15T14:30:00+05:30',
        latitude: 19.0760,
        longitude: 72.8777
    })
});

const birthChart = await response.json();
console.log(birthChart.planets, birthChart.houses, birthChart.yogas);