# Synastry API

> Synastry API. Calculate complete synastry (relationship compatibility) between two natal charts using Western tropical astrology. Analyzes inter-chart

- Capability page: https://roxyapi.com/apis/synastry-api
- Full domain: https://roxyapi.com/products/astrology-api
- OpenAPI spec: https://roxyapi.com/api/v2/astrology/openapi.json
- Remote MCP server: https://roxyapi.com/mcp/astrology

## Overview

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.

## Endpoints

- `POST /api/v2/astrology/synastry` Calculate synastry - Relationship compatibility analysis API
- `POST /api/v2/astrology/compatibility-score` Compatibility Score. Relationship compatibility analysis with category breakdown

## Example request

```bash
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}}'
```

## Example response

```json
{
  "person1": {
    "ascendant": {
      "sign": "Taurus",
      "degree": 15.32
    },
    "sunSign": "Cancer",
    "moonSign": "Pisces"
  },
  "person2": {
    "ascendant": {
      "sign": "Virgo",
      "degree": 22.18
    },
    "sunSign": "Pisces",
    "moonSign": "Scorpio"
  },
  "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": "string",
    "strengths": [
      "string"
    ],
    "challenges": [
      "string"
    ]
  }
}
```

## Remote MCP

Every endpoint is a callable tool on the Remote MCP server at https://roxyapi.com/mcp/astrology over Streamable HTTP. Tool name for `POST /astrology/synastry`: `post_astrology_synastry`. `tools/list` is free; `tools/call` bills the same as REST.

## FAQ

### What does the Synastry API return?

Calculate complete synastry (relationship compatibility) between two natal charts using Western tropical astrology. Every response is structured JSON with documented fields, not free text, so you map it straight into your product.

### How do I authenticate with the Synastry API?

Pass your key in the X-API-Key header on every request. Keys are delivered instantly at checkout with no approval queue. Use a secret sk key server side, or mint a publishable pk key locked to your origins for browser and no-code use.

### Does the Synastry API support multiple languages?

Yes. Append the lang query parameter to any endpoint for responses in English, German, Spanish, French, Hindi, Portuguese, Russian and Turkish. The translated payload includes the full interpretation text, not just field labels.

### Do I need coordinates to call the Synastry API?

No. Call GET /location/search with a city name first, then pass latitude, longitude, and timezone from the first result into the request. Never ask users to type coordinates. Timezone accepts a decimal offset or an IANA name.

### Is the Synastry API available over Remote MCP for AI agents?

Yes. Every endpoint is exposed as a callable tool on the Remote MCP server at https://roxyapi.com/mcp/astrology over Streamable HTTP, so Claude, ChatGPT, Cursor, and any MCP client auto-discover it with no local setup or Docker.

### How is the Synastry API billed?

Flat pricing: 1 request equals 1 quota unit, REST and MCP identical, with no credit weighting or per-token markup. Every plan includes all 12 domains, so the Synastry API is included at no extra cost.

### What lang values does the Synastry API accept?

The lang parameter accepts en, tr, de, es, hi, pt, fr, ru. Case-insensitive where it is a path value.

## Full reference

Fetch the OpenAPI spec at https://roxyapi.com/api/v2/astrology/openapi.json. Master agent manifest at https://roxyapi.com/llms.txt.