What is the difference between JSON formatting and validation?

Formatting (or prettifying) adds indentation and line breaks to make JSON human-readable. Validation checks whether the JSON is syntactically correct — balanced braces, properly quoted keys, correct value types, no trailing commas. A JSON file can be valid but still poorly formatted, or well-formatted but invalid.

What are common JSON syntax errors?

The most common JSON errors are: trailing commas after the last item in an object or array, single quotes instead of double quotes around keys/strings, unquoted keys, comments (JSON does not support comments), undefined or NaN values, and missing or extra curly braces/square brackets.

When should I minify JSON?

Minify JSON when it will be sent over a network (API responses, config downloads) to reduce payload size. Pretty-print JSON when writing config files, storing in version control, or when humans need to read or edit it. Production API responses benefit from minification, but logged or stored JSON should remain readable.

JSON Formatter & Validator Online

Paste your JSON to format, validate, and beautify it with proper indentation. Detects syntax errors and supports minification. All processing happens in your browser.

What Is JSON?

JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format defined by RFC 8259. It is human-readable and language-independent, making it the standard format for REST APIs, configuration files, and data storage across nearly all programming ecosystems.

JSON Data Types

Type	Example	Notes
String	`"hello"`	Must use double quotes. Escape special chars with `\`
Number	`42`, `3.14`, `-1e10`	No quotes. No NaN or Infinity
Boolean	`true`, `false`	Lowercase only
Null	`null`	Lowercase only
Object	`{"key": "value"}`	Unordered key-value pairs. Keys must be strings
Array	`[1, 2, 3]`	Ordered list of any values

Common JSON Syntax Errors

Trailing comma: {"a": 1, "b": 2,} — the comma after 2 is invalid in JSON (but valid in JavaScript).
Single quotes: {'key': 'value'} — JSON requires double quotes for strings and keys.
Unquoted keys: {key: "value"} — all keys must be quoted strings.
Comments: JSON does not support // or /* */ comments. Use JSON5 or JSONC if you need comments.
NaN / Infinity: These JavaScript values are not valid JSON. Use null or a sentinel number instead.
Unescaped control characters: Literal newlines inside strings are invalid — use \n instead.

JSON Formatting in Code

JavaScript / Node.js

// Pretty print with 2-space indent
const formatted = JSON.stringify(data, null, 2);

// Minify
const minified = JSON.stringify(data);

// Parse and re-format API response
const pretty = JSON.stringify(JSON.parse(responseText), null, 2);

Python

import json

# Pretty print
print(json.dumps(data, indent=2, sort_keys=True))

# Minify
print(json.dumps(data, separators=(',', ':')))

Shell (Linux/macOS)

# Format JSON file with jq
jq . data.json

# Minify
jq -c . data.json

# Extract a nested value
jq '.user.address.city' data.json

JSON Schema Validation

JSON Schema is a vocabulary for annotating and validating JSON documents. It lets you define the expected structure, types, and constraints of your JSON data, enabling automated validation at API boundaries or in CI pipelines.

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "properties": {
    "name": { "type": "string", "minLength": 1 },
    "age":  { "type": "integer", "minimum": 0 }
  },
  "required": ["name"]
}

Best Practices

Use 2-space indentation for configuration files stored in version control — it is the most common convention.
Sort keys alphabetically in config files to reduce diff noise when keys are added or removed.
Minify JSON in production API responses to reduce payload size and improve latency.
Validate JSON against a schema at API entry points to fail fast on malformed input.
Use JSON.parse in a try/catch block — never assume input is valid JSON.