Synastry API

Calculate complete synastry (relationship compatibility) between two natal charts using Western tropical astrology. Analyzes inter-chart aspects between all planets to determine romantic, friendship, and karmic compatibility. Returns compatibility score (0-100), detailed inter-aspects with strength ratings, harmonious vs challenging aspect counts, and relationship dynamics analysis. Perfect for dating apps, matrimonial sites, relationship counseling tools, and astrology compatibility features. Based on professional astrological techniques.

Request

POST /api/v2/astrology/synastry

{
  "person1": {
    "date": "1990-07-15",
    "time": "14:30:00",
    "latitude": 40.7128,
    "longitude": -74.006,
    "timezone": -5
  },
  "person2": {
    "date": "1990-07-15",
    "time": "14:30:00",
    "latitude": 40.7128,
    "longitude": -74.006,
    "timezone": -5
  }
}

Response

Structured JSON with documented fields, covered by 6,991 automated tests per deploy, 1,527 of them gold-standard tests verified against NASA JPL Horizons. Not hallucinated text.

{
  "person1": {
    "ascendant": {
      "sign": "Taurus",
      "degree": 15.32
    },
    "sunSign": "Cancer",
    "moonSign": "Pisces",
    "planets": [
      {
        "name": "Sun",
        "longitude": 114.52,
        "sign": "Cancer",
        "degree": 24.52,
        "house": 3,
        "isRetrograde": false
      }
    ]
  },
  "person2": {
    "ascendant": {
      "sign": "Virgo",
      "degree": 22.18
    },
    "sunSign": "Pisces",
    "moonSign": "Scorpio",
    "planets": [
      {
        "name": "Sun",
        "longitude": 114.52,
        "sign": "Cancer",
        "degree": 24.52,
        "house": 3,
        "isRetrograde": false
      }
    ]
  },
  "compatibilityScore": 78,
  "interAspects": [
    {
      "planet1": "Venus",
      "planet2": "Mars",
      "type": "TRINE",
      "angle": 120,
      "orb": 2.5,
      "strength": 75,
      "interpretation": "harmonious"
    }
  ],
  "summary": {
    "total": 24,
    "harmonious": 12,
    "challenging": 8,
    "neutral": 4,
    "byType": {
      "TRINE": 5,
      "SEXTILE": 7,
      "SQUARE": 6,
      "OPPOSITION": 2
    }
  },
  "analysis": {
    "overall": "This relationship shows strong compatibility with genuine potential for lasting partnership. Most interactions feel natural and supportive, with a healthy mix of comfort and growth. Where challenges arise, both partners have the tools to work through them constructively.",
    "strengths": [
      "More harmonious aspects than challenging ones create a supportive foundation.",
      "Harmonious Moon aspects indicate emotional understanding and nurturing.",
      "Favorable Venus aspects bring affection, appreciation, and romantic chemistry."
    ],
    "challenges": [
      "Challenging Sun aspects may create ego conflicts or competing life directions.",
      "Challenging Mars aspects may bring tension, arguments, or competing desires."
    ]
  }
}

Supported options

Call it in your language in seconds.

Every snippet is generated from the live OpenAPI spec, so method names, parameters, and fields always match production.

import { createRoxy } from '@roxyapi/sdk'

const roxy = createRoxy(process.env.ROXY_API_KEY!)
const { data } = await roxy.astrology.calculateSynastry({ body: { person1: { date: '1990-07-15', time: '14:30:00', latitude: 40.7128, longitude: -74.006, timezone: -5 }, person2: { date: '1990-07-15', time: '14:30:00', latitude: 40.7128, longitude: -74.006, timezone: -5 } } })

from roxy_sdk import create_roxy

roxy = create_roxy("YOUR_API_KEY")
result = roxy.astrology.calculate_synastry(person1={'date': '1990-07-15', 'time': '14:30:00', 'latitude': 40.7128, 'longitude': -74.006, 'timezone': -5}, person2={'date': '1990-07-15', 'time': '14:30:00', 'latitude': 40.7128, 'longitude': -74.006, 'timezone': -5})

use function RoxyAPI\Sdk\createRoxy;

$roxy = createRoxy(getenv('ROXY_API_KEY'));
$result = $roxy->astrology->calculateSynastry(person1: ['date' => '1990-07-15', 'time' => '14:30:00', 'latitude' => 40.7128, 'longitude' => -74.006, 'timezone' => -5], person2: ['date' => '1990-07-15', 'time' => '14:30:00', 'latitude' => 40.7128, 'longitude' => -74.006, 'timezone' => -5]);

using RoxyApi;

var roxy = new RoxyClient(Environment.GetEnvironmentVariable("ROXY_API_KEY")!);
var result = await roxy.Astrology.Synastry.PostAsync(new() { /* request fields above */ });

import roxyapi "github.com/RoxyAPI/sdk-go"

roxy, _ := roxyapi.NewRoxy(os.Getenv("ROXY_API_KEY"))
resp, _ := roxy.Astrology.CalculateSynastry(ctx, nil, roxyapi.CalculateSynastryJSONRequestBody{ /* request fields above */ })

curl -X POST "https://roxyapi.com/api/v2/astrology/synastry" \
  -H "X-API-Key: YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{"person1":{"date":"1990-07-15","time":"14:30:00","latitude":40.7128,"longitude":-74.006,"timezone":-5},"person2":{"date":"1990-07-15","time":"14:30:00","latitude":40.7128,"longitude":-74.006,"timezone":-5}}'

More Synastry endpoints

The Synastry API bundles these related endpoints under one key.

Remote MCP for AI agents

Every Western Astrology endpoint is a callable tool on the Remote MCP server over Streamable HTTP. No local setup, no Docker. Claude, ChatGPT, Cursor, and any MCP client auto-discover the tools and ground their answers in verified data.

claude mcp add --transport http \
  roxy-astrology https://roxyapi.com/mcp/astrology \
  --header "X-API-Key: YOUR_KEY"

Tool name for POST /astrology/synastry: post_astrology_synastry. Full MCP setup guide

What you can build

Drop-in UI components & widgets

Render Synastry API responses without building charts yourself. Install the npm package and drop these into Next.js, React, Vue, Svelte, Angular, or plain HTML, or embed the very same component on Squarespace, Wix, or WordPress by pasting one snippet, with no backend and no build step. They belong to one library that covers the entire spiritual stack rather than astrology alone, MIT licensed and included in every plan at no extra cost, never a separate product and never an upsell. The Synastry API calculations, the interface that renders them, and the Remote MCP your agent calls, all behind one key, end to end.

Synastry chart widget snippetCompatibility card widget snippetThe complete UI libraryExplore Roxy UI

Related capabilities

Synastry API FAQ