JSON Syntax

Definition and Usage

JSON syntax is how you write structured data as text: curly braces for objects, square brackets for arrays, and "key": value pairs with double quotes.

Nest objects and arrays to model real API payloads. For the hard “must / must not” checklist (trailing commas, comments), see JSON Rules. For the six value kinds, see JSON Data Types.

Building Blocks

• object { } holds named properties — {"id": 1}
• array [ ] holds an ordered list — [1, 2, 3]
• key : value Inside an object: quoted key, colon, then any JSON value
• string Always double quotes — "Ada"
• nesting Objects and arrays can contain other objects and arrays
• commas Separate siblings; never after the last item

Full Structure

A typical record: an object with a nested object and an array.

{
  "name": "Ada",
  "age": 36,
  "active": true,
  "address": {
    "city": "London",
    "zip": "SW1A"
  },
  "skills": ["math", "code"]
}

Describing Structure

Once the text follows JSON syntax, JSON Schema can name the expected shape—object vs array, required keys, nested properties.

{
  "type": "object",
  "required": ["name", "skills"],
  "properties": {
    "name": { "type": "string" },
    "address": { "type": "object" },
    "skills": {
      "type": "array",
      "items": { "type": "string" }
    }
  }
}

Examples

Use View Output for a quick result, or Try It Yourself to edit and run in the browser.

const text = `{
  "name": "Ada",
  "address": { "city": "London" },
  "skills": ["math", "code"]
}`;

const user = JSON.parse(text);
console.log(user.name);
console.log(user.address.city);
console.log(user.skills[1]);

Ada
London
code

const user = {
  name: "Ada",
  address: { city: "London", zip: "SW1A" },
  skills: ["math", "code"]
};

console.log(user.address.zip);
console.log(user.skills.length);
console.log(user.skills.join(", "));

SW1A
2
math, code

const text = `[
  { "id": 1, "name": "Ada" },
  { "id": 2, "name": "Grace" }
]`;

const list = JSON.parse(text);
console.log(list.length);
console.log(list[0].name);
console.log(list[1].id);

2
Ada
2