# Hexagram Compatibility

`POST https://api.astroway.info/v1/iching/compatibility`

Compares two hexagrams: matching and differing lines, named relations (identical, complement, inverse, nuclear, shared or swapped trigrams), five-phase relations of the lower and of the upper trigrams, and a 0-100 score whose formula is stated in the response (a convention of this API, not a classical measure).

Group: I Ching (Standalone). Auth: `X-Api-Key` header. Operation ID: `iching_compatibility`.

## Parameters

| Name | In | Required | Type | Description |
|---|---|---|---|---|
| `fields` | query | no | string | Comma-separated dotted paths, relative to `data`, to keep in the response. A path is applied to every element of an array, so `planets.name` means the name of each planet. Paths that match nothing come back in `_fields_unmatched`; a list where nothing matches at all is a 400, because an empty object would be a confident wrong answer. |
| `precision` | query | no | integer | Round every non-integer number in the response to this many decimal places. Integers are left alone, because an id is not a measurement. Ecliptic longitudes ship with fourteen decimals by default; 2 is about a tenth of an arcminute. |
| `Idempotency-Key` | header | no | string | Unique per logical operation, kept across retries. For 24 hours from the first request, a repeat with the same key, method, path, body and query string returns the stored response with `Idempotent-Replayed: true` and costs 0 credits. The same key with a different body or query string is a 409 `IDEMPOTENCY_KEY_REUSED`; a repeat while the first is still running is a 409 `IDEMPOTENCY_IN_PROGRESS`. Only 2xx responses are kept. See /idempotency/. |

## Request body

| Field | Type | Required | Description |
|---|---|---|---|
| `hexagramA` | integer | yes | King Wen number of the first hexagram. |
| `hexagramB` | integer | yes | King Wen number of the second hexagram. |

```json
{
  "hexagramA": 11,
  "hexagramB": 12
}
```

## Responses

| Status | Meaning |
|---|---|
| 200 | Successful calculation |
| 400 | Validation error |
| 401 | Missing or invalid API key |

### Success fields, under `data`

| Field | Type | Required | Description |
|---|---|---|---|
| `a` | object | no |  |
| `a.number` | number | no |  |
| `a.name` | string | no |  |
| `a.pinyin` | string | no |  |
| `a.legge` | string | no |  |
| `a.chinese` | string | no |  |
| `a.lines` | number[] | no |  |
| `a.lowerTrigram` | number | no |  |
| `a.upperTrigram` | number | no |  |
| `a.judgment` | string | no |  |
| `b` | object | no |  |
| `b.number` | number | no |  |
| `b.name` | string | no |  |
| `b.pinyin` | string | no |  |
| `b.legge` | string | no |  |
| `b.chinese` | string | no |  |
| `b.lines` | number[] | no |  |
| `b.lowerTrigram` | number | no |  |
| `b.upperTrigram` | number | no |  |
| `b.judgment` | string | no |  |
| `matchingLines` | number | no |  |
| `differingLines` | number[] | no |  |
| `relations` | string[] | no |  |
| `phases` | object | no |  |
| `phases.lower` | object | no |  |
| `phases.upper` | object | no |  |
| `score` | number | no |  |
| `scoreRule` | string | no |  |
| `source` | string | no |  |

## Example

```bash
curl -X POST https://api.astroway.info/v1/iching/compatibility \
  -H "X-Api-Key: aw_live_..." \
  -H "Content-Type: application/json" \
  -d '{ "hexagramA": 11, "hexagramB": 12 }'
```

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Rendered from https://api.astroway.info/v1/openapi.json. HTML page: https://api.astroway.info/docs/api/operations/iching_compatibility/