What Is JSON?

JSON stands for JavaScript Object Notation. It is a lightweight text format used to send structured data between systems, especially web apps, APIs, integration platforms, and test tools.

JSON in plain language

A JSON payload stores data as name and value pairs. It can contain objects, arrays, strings, numbers, booleans, and empty values. Humans can read it, and software can parse it quickly.

{
  "poNumber": "123456",
  "customer": "ACME Warehouse",
  "items": [
    { "sku": "ABC123", "quantity": 10 }
  ]
}

A full JSON file example

This example represents one purchase order. The full file is one JSON object with order-level fields and a list of line items.

{
  "poNumber": "123456",
  "orderDate": "2026-05-05",
  "shipTo": {
    "name": "ACME Warehouse",
    "city": "Dallas",
    "state": "TX"
  },
  "items": [
    {
      "sku": "ABC123",
      "quantity": 10,
      "unitPrice": 15.25
    },
    {
      "sku": "XYZ789",
      "quantity": 4,
      "unitPrice": 7.5
    }
  ]
}

The main parts of JSON

Objects are wrapped in curly braces. An object groups related fields together, such as one order, one customer, or one item.

Names, often called keys or fields, appear on the left side of a colon. In the example, poNumber, customer, items, sku, and quantity are names.

Values appear on the right side of a colon. A value can be text, a number, true or false, null, another object, or an array.

Arrays are wrapped in square brackets. Arrays hold a list of values or objects. In integration work, arrays often represent order lines, packages, addresses, notes, or status records.

Highlighted JSON parts

Object example: the blue curly braces wrap one related area of data.

{
  "name": "ACME Warehouse",
  "city": "Dallas"
}

Name example: the yellow text is the field name. It tells you what the value means.

{
  "poNumber": "123456"
}

Value example: the green text is the value assigned to the name.

{
  "quantity": 10,
  "sku": "ABC123"
}

Array example: the pink square brackets hold a list. Here the list contains two item objects.

"items": [
  { "sku": "ABC123", "quantity": 10 },
  { "sku": "XYZ789", "quantity": 4 }
]

How to read a JSON payload

Start with the outer object, then move inward through each nested area. If you see a name followed by a simple value, that is a direct field. If you see a name followed by curly braces, that field contains another object. If you see a name followed by square brackets, that field contains a list.

Good field names make a JSON payload easier to understand. Names like shipTo, orderDate, trackingNumber, and lineItems tell a reader what business area each value belongs to.

Why teams format JSON

APIs often return compact JSON with no line breaks. Formatting turns that compact text into readable rows and indentation, which helps developers and QA testers verify fields, arrays, and nested values.

Formatting does not change the meaning of valid JSON. It changes the layout so people can inspect it more easily.

Why JSON comparison matters

JSON payloads change during API releases, partner onboarding, and test automation. A comparison can reveal missing fields, renamed values, changed quantities, or extra array items before a change reaches production.

USA Data Tools lets teams paste JSON, format it, create repeatable loops, and compare payloads in the browser.