JSON Objects, Arrays, and Value Types Explained with Real Examples

Despite powering almost the entire internet's API ecosystem, JSON is remarkably minimalist. Defined formally by RFC 8259, the JSON grammar permits exactly six data types.

While modern programming languages like TypeScript, Python, and Rust feature hundreds of rich types (enums, tuples, sets, maps, decimals, and dates), transferring data across the wire requires mapping everything into these six universal primitives.

In this guide, you will explore how each JSON data type works, inspect real-world examples, avoid common type conversion pitfalls, and learn how to inspect types visually.

The 6 Universal JSON Data Types

1. Object (`{}`)

An object is an unordered collection of zero or more key-value pairs wrapped in curly braces.

• Rule: Every key must be a string enclosed in double quotes (").
• Rule: Keys must be separated from values by a colon (:).
• Rule: Key-value pairs must be separated by commas (,).

{
  "user_id": 1092,
  "username": "alex_codes",
  "verified": true
}

2. Array (`[]`)

An array is an ordered sequence of zero or more values enclosed in square brackets.

• Rule: Elements are zero-indexed ([0], [1], [2]).
• Rule: Arrays can store mixed types, including nested objects and other arrays.

[
  "first",
  42,
  false,
  null,
  { "nested": "object" }
]

3. String (`""`)

A string is a sequence of zero or more Unicode characters wrapped in double quotes (").

• Rule: Single quotes (') are strictly forbidden.
• Rule: Special characters must be escaped with a backslash (e.g., \", \\, \n, \t).

{
  "title": "Senior Frontend Engineer",
  "quote": "Code is poetry, \"clean\" code is art.",
  "unicode_flag": "\u2600 Sun"
}

4. Number

JSON numbers can be integers, fractions, or exponential scientific notations.

• Rule: Numbers cannot have leading zeros (e.g., 052 is illegal; write 52).
• Rule: NaN, Infinity, and -Infinity are strictly forbidden.
• Rule: Hexadecimal literals (0x1F) and octals are illegal.

{
  "integer": 42,
  "negative": -18,
  "decimal": 3.14159,
  "scientific": 1.25e+4
}

5. Boolean (`true` / `false`)

JSON booleans represent binary truth values.

• Rule: Must be lowercase literal true or false.
• Rule: Capitalized True, False, or string "true" are not boolean values.

{
  "is_admin": true,
  "email_verified": false
}

6. Null (`null`)

null represents an intentionally empty or non-existent value.

• Rule: Must be lowercase literal null.
• Rule: Distinct from 0, false, or an empty string "".

{
  "middle_name": null,
  "deleted_at": null
}

4 Things Developers Try to Put in JSON (That Fail!)

If you write full-stack JavaScript or Python, it is tempting to pass language features directly to JSON. Here is why they break:

Inspecting Types Visually with UtilityKit

When inspecting a large JSON file, distinguishing between string numbers ("42" vs 42) or string booleans ("true" vs true) in raw text is tedious.

UtilityKit's JSON Tools highlights types automatically:

1. Tree Viewer Mode: Badges each node as STR, NUM, BOOL, NULL, OBJ, or ARR with dedicated color accents.
2. Visual Editor Mode: Provides a type selector dropdown next to every key, letting you convert types safely without breaking quotes or brackets.