Synastry APIRelationship Scoring & Insights

Instantly calculate full compatibility between two birth charts. Get quantified scores across six core domains, pre-written narratives, and ranked astrological aspects.

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Built with this API

See the Synastry API in action. We built a fully featured, open-source relationship astrology app in Next.js using exactly these endpoints.

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Built for Mobile UI Focus

The API does the heavy lifting, giving you data structures perfectly mapped to modern mobile cards and visual widgets.

6-Domain Scoring System

Avoid vague interpretations. We calculate numeric scores (0-100) for Romance, Communication, Chemistry, Intimacy, Partnership, and Shared Growth based on weighted planetary aspects.

Synastry Bands™

Get three deterministic string narratives (`bond_tone`, `core_dynamic`, and `watch_for`) derived directly from the relationship's strongest and weakest aspects.

Ranked & Ready Aspects

The `aspects` array returns all active transits pre-sorted by `strength` (percentile 0.0-1.0), with explicit polarity (`supportive` vs `challenging`) so you don't guess what to render first.

Simple Integration

A single POST request takes birth data for two individuals, doing complex intersection analysis on the fly and returning a unified summary block.

Smart Timezone Handling

Pass `tz_str: "AUTO"` and the exact city name — we resolve coordinates and timezone shifts automatically.

14 Core Archetypes

Relationships are automatically classified into one of 14 deterministic archetypes like "Soulmate Connection" or "Karmic Mirror".

High Precision Orbs

POST /api/v1/western/synastrycards

{
  "summary": {
    "archetype": {
      "id": "twin_flame",
      "label": "Twin Flame",
      "one_liner": "An intense, mirroring connection."
    },
    "scores": {
      "overall": 88,
      "romance": 92,
      "communication": 85,
      "intimacy": 95,
      "partnership": 80,
      "shared_growth": 90
    },
    "bands": {
      "bond_tone": "A deeply romantic connection...",
      "core_dynamic": "You intuitively understand...",
      "watch_for": "Be mindful of getting too lost..."
    }
  }
}

Synastry API FAQ

Can this be used for business or friendships?

Currently, the textual interpretation blocks and bands returned by this endpoint are specifically tuned for **romantic relationships**. We will be adding friendship and business modes in the near future.

How do the scores work?

The engine calculates all valid inter-aspects between the two entire charts, scales each aspect's weight by its orb tightness and base significance, and distributes the impact across relevant domains. The result is mapped to an intuitive 0-100 benchmark.

Is the old Synastry Grid still available?

Yes, the /api/v1/western/synastry endpoint remains fully supported if you need the raw calculation matrix of intersecting planet positions instead of pre-computed UI blocks.

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