JSON Formatting Guide — How to Read, Write, and Validate JSON

JSON (JavaScript Object Notation) is the universal language of web APIs. Whether you are building a web app, calling a REST API, or writing a configuration file, you will work with JSON constantly. This guide covers everything from basic syntax to debugging common errors.

JSON Syntax Rules

JSON has strict syntax requirements — a single missing comma or extra bracket will break everything.

{
  "name": "Pradeep",
  "age": 42,
  "active": true,
  "score": null,
  "tags": ["developer", "devops"],
  "address": {
    "city": "Stockholm",
    "country": "Sweden"
  }
}

• Keys must be double-quoted strings — single quotes are not valid JSON
• String values must use double quotes
• No trailing commas after the last item in an object or array
• No comments — JSON does not support // comments
• Numbers, booleans (true/false), and null are unquoted

Formatting vs Minifying

Formatted (pretty-printed)

Indented with spaces or tabs for human readability. Use when debugging or reading API responses.

Minified

All whitespace removed. Used in production to reduce file size and improve transfer speeds. A minified JSON file can be 20–40% smaller.

// Formatted (28 bytes)
{
  "name": "Alice"
}

// Minified (16 bytes)
{"name":"Alice"}

Common JSON Errors and How to Fix Them

Trailing comma

// INVALID — trailing comma after last item
{
  "name": "Alice",
  "age": 30,  ← remove this comma
}

// VALID
{
  "name": "Alice",
  "age": 30
}

Single quotes

// INVALID
{'name': 'Alice'}

// VALID
{"name": "Alice"}

Unquoted keys

// INVALID (JavaScript object notation, not JSON)
{name: "Alice"}

// VALID
{"name": "Alice"}

Parsing JSON in Code

JavaScript

const jsonString = '{"name": "Alice", "age": 30}';
const obj = JSON.parse(jsonString);
console.log(obj.name); // → "Alice"

// Convert back to JSON string
const str = JSON.stringify(obj, null, 2); // null, 2 = pretty print

Python

import json

json_string = '{"name": "Alice", "age": 30}'
data = json.loads(json_string)
print(data["name"])  # → Alice

# Convert back
formatted = json.dumps(data, indent=2)