Compare

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.

Updated October 27, 2026

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.

{
  "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

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

$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

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

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

// 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

// 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

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.

{
  "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