JSON Syntax Basics

Every JSON document is built from a small set of punctuation rules. Once you internalize them, invalid files become much easier to fix.

Two structural forms

JSON values are either:

• An object — wrapped in { }, containing key–value pairs
• An array — wrapped in [ ], containing an ordered list of values

A file can be a single object, a single array, or (less commonly) a single primitive value like "hello" or 42.

Objects: keys and colons

Inside an object, each entry looks like:

"key": value

Rules:

• Keys must be double-quoted strings
• A colon : separates the key from its value
• Commas , separate entries—but never after the last one

{
  "id": 1,
  "label": "primary"
}

Arrays: ordered values

Arrays list values without keys:

["red", "green", "blue"]

Mixed types are allowed in one array (unlike some typed languages), though APIs often keep arrays homogeneous.

Nesting

Objects and arrays can contain each other without limit:

{
  "users": [
    { "id": 1, "roles": ["admin", "editor"] },
    { "id": 2, "roles": ["viewer"] }
  ]
}

Whitespace

Spaces, tabs, and line breaks outside strings are insignificant. Formatting is for humans; parsers ignore extra whitespace.

Valid top-level shapes

Valid	Invalid
{ ... }	{ key: "x" } (unquoted key)
[ ... ]	'string' (single quotes)
"text", 42, true, null	{ "a": 1, } (trailing comma)

The next lesson covers each value type in detail.