# List what changed between two JSON documents

`POST /v1/compare/json`

Returns every added, removed and changed path with the old and new values. Key order does not matter and identical documents give an empty list. Arrays are compared by position, or by a property when array_key is given, so a reordered list is not reported as a change.

## Request body

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| first | any | yes | The original document |
| second | any | yes | The document to compare it with |
| array_key | string | no | Match the objects of arrays by this property instead of by position, so a reordered list is not a change |

## Example request

A request body that works, as JSON.

```json
{
  "first": {
    "city": "Porto",
    "total": 10.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ]
  },
  "second": {
    "city": "Porto",
    "total": 12.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ],
    "coupon": "WELCOME"
  },
  "array_key": "id"
}
```

## Code samples

Replace YOUR_TOKEN with your access token.

### curl

```shell
curl -X POST 'https://api.skillfulsardine.com/v1/compare/json' \
  -H 'Authorization: Bearer YOUR_TOKEN' \
  -H 'Content-Type: application/json' \
  --data-raw '{
  "first": {
    "city": "Porto",
    "total": 10.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ]
  },
  "second": {
    "city": "Porto",
    "total": 12.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ],
    "coupon": "WELCOME"
  },
  "array_key": "id"
}'
```

### PowerShell

```powershell
$body = @'
{
  "first": {
    "city": "Porto",
    "total": 10.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ]
  },
  "second": {
    "city": "Porto",
    "total": 12.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ],
    "coupon": "WELCOME"
  },
  "array_key": "id"
}
'@
$response = Invoke-RestMethod -Method Post -Uri 'https://api.skillfulsardine.com/v1/compare/json' `
  -Headers @{ Authorization = 'Bearer YOUR_TOKEN' } `
  -ContentType 'application/json; charset=utf-8' `
  -Body ([System.Text.Encoding]::UTF8.GetBytes($body))
$response | ConvertTo-Json -Depth 10
```

### Python

```python
import requests

payload = {
    "first": {
        "city": "Porto",
        "total": 10.0,
        "items": [
            {
                "id": "A1",
                "qty": 1,
            },
        ],
    },
    "second": {
        "city": "Porto",
        "total": 12.0,
        "items": [
            {
                "id": "A1",
                "qty": 1,
            },
        ],
        "coupon": "WELCOME",
    },
    "array_key": "id",
}

response = requests.post(
    "https://api.skillfulsardine.com/v1/compare/json",
    headers={"Authorization": "Bearer YOUR_TOKEN"},
    json=payload,
    timeout=30,
)
print(response.json())
```

### JavaScript

```javascript
const response = await fetch("https://api.skillfulsardine.com/v1/compare/json", {
  method: "POST",
  headers: {
    "Authorization": "Bearer YOUR_TOKEN",
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
  "first": {
    "city": "Porto",
    "total": 10.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ]
  },
  "second": {
    "city": "Porto",
    "total": 12.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ],
    "coupon": "WELCOME"
  },
  "array_key": "id"
}),
});
const result = await response.json();
console.log(result);
```

### Node

```javascript
// Node 18 or later. Save as call.mjs and run: API_TOKEN=... node call.mjs
const token = process.env.API_TOKEN;

const response = await fetch("https://api.skillfulsardine.com/v1/compare/json", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${token}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
  "first": {
    "city": "Porto",
    "total": 10.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ]
  },
  "second": {
    "city": "Porto",
    "total": 12.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ],
    "coupon": "WELCOME"
  },
  "array_key": "id"
}),
});
const result = await response.json();
console.log(result);
```

### Rust

```rust
// Cargo.toml: reqwest = { version = "0.12", features = ["blocking", "json"] }, serde_json = "1"
fn main() -> Result<(), Box<dyn std::error::Error>> {
    let body: serde_json::Value = serde_json::from_str(r#"{
  "first": {
    "city": "Porto",
    "total": 10.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ]
  },
  "second": {
    "city": "Porto",
    "total": 12.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ],
    "coupon": "WELCOME"
  },
  "array_key": "id"
}"#)?;
    let response = reqwest::blocking::Client::new()
        .post("https://api.skillfulsardine.com/v1/compare/json")
        .bearer_auth("YOUR_TOKEN")
        .json(&body)
        .send()?;
    println!("{}", response.text()?);
    Ok(())
}
```

### Swift

```swift
import Foundation

var request = URLRequest(url: URL(string: "https://api.skillfulsardine.com/v1/compare/json")!)
request.httpMethod = "POST"
request.setValue("Bearer YOUR_TOKEN", forHTTPHeaderField: "Authorization")
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpBody = Data(#"""
{
  "first": {
    "city": "Porto",
    "total": 10.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ]
  },
  "second": {
    "city": "Porto",
    "total": 12.0,
    "items": [
      {
        "id": "A1",
        "qty": 1
      }
    ],
    "coupon": "WELCOME"
  },
  "array_key": "id"
}
"""#.utf8)

let (data, _) = try await URLSession.shared.data(for: request)
print(String(decoding: data, as: UTF8.self))
```

## Response

The fields inside `data` of a successful response.

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| identical | boolean | yes | True when there is no difference |
| changes | array of JsonChange | yes | Every difference, in document order |
| change_count | integer | yes | Number of differences |

## Example response

A real answer from the operation, as JSON. The fields in the table above are inside `data`.

```json
{
  "data": {
    "identical": false,
    "changes": [
      {
        "path": "total",
        "type": "changed",
        "old": 10.0,
        "new": 12.0
      },
      {
        "path": "coupon",
        "type": "added",
        "old": null,
        "new": "WELCOME"
      }
    ],
    "change_count": 2
  },
  "errors": null,
  "meta": {
    "request_id": "4c08c31f-b392-4468-a89b-c0b13c099e70",
    "timestamp": "2026-10-27T07:19:42.113655Z",
    "version": "2026-03-26"
  },
  "pagination": null
}
```

## Responses

| Status | When it happens |
| --- | --- |
| 200 | Successful Response |
| 400 | The body respects the operation schema, but the use case rejected it. Each problem is one ApiError entry |
| 413 | The request is larger than the request size limit of the API allows |
| 422 | The body does not respect the operation schema. Each problem is one ApiError entry with the code validation_error |
| 500 | Something failed inside the server and was not an input problem. The same envelope, errors may be empty |

---
Source: https://skillfulsardine.com/developers/api/diff-json/