> ## Documentation Index
> Fetch the complete documentation index at: https://docs.pidgeon.health/llms.txt
> Use this file to discover all available pages before exploring further.

# Compare Messages

> Compare two healthcare messages field-by-field via the Bridge API.

## POST /api/diff

Compare two messages and return field-level differences. **Public** — no authentication required.

### Request Body

| Field           | Type      | Default     | Description                                     |
| --------------- | --------- | ----------- | ----------------------------------------------- |
| `leftMessage`   | string    | Required    | Baseline message                                |
| `rightMessage`  | string    | Required    | Comparison message                              |
| `standard`      | string    | Auto-detect | `hl7`, `fhir`, `ncpdp`                          |
| `ignoredFields` | string\[] | `[]`        | Fields to exclude (e.g., `["PID.3", "MSH.10"]`) |

### Example

```bash curl theme={null}
curl -X POST http://localhost:5101/api/diff \
  -H "Content-Type: application/json" \
  -d '{
    "leftMessage": "MSH|^~\\&|SENDER|FAC|RECV|DEST|20260222||ADT^A01|12345|P|2.3\rPID|1||MRN001^^^MRN||DOE^JOHN||19800101|M",
    "rightMessage": "MSH|^~\\&|SENDER|FAC|RECV|DEST|20260222||ADT^A01|12345|P|2.3\rPID|1||MRN001^^^MRN||DOE^JANE||19800101|F",
    "standard": "hl7",
    "ignoredFields": ["MSH.10"]
  }'
```

### Response

```json theme={null}
{
  "success": true,
  "data": {
    "differences": [
      {
        "field": "PID.5.1",
        "leftValue": "JOHN",
        "rightValue": "JANE",
        "changeType": "modified"
      },
      {
        "field": "PID.8",
        "leftValue": "M",
        "rightValue": "F",
        "changeType": "modified"
      }
    ],
    "totalDifferences": 2,
    "ignoredFields": ["MSH.10"]
  },
  "error": null
}
```