JSON Formatter & Validator

Structuring, Validating & Formatting JSON Data

JavaScript Object Notation (JSON), standardized under RFC 8259 and ECMA-404, is the de facto standard data interchange format for modern REST APIs, microservice architectures, and configuration files. Formatting and linting JSON transforms dense, minified payload strings into clearly indented, human-readable representations while detecting syntactic errors.

The Six Native JSON Data Types

JSON grammar strictly supports six primitive and composite data structures:

Data Type	Syntax Example	Technical Rules & Constraints
String	"username": "alice"	Must be enclosed in double quotes; backslash escapes permitted
Number	"count": 42, "ratio": 3.1415	Decimals permitted; octal, hex (0x), and NaN are strictly invalid
Boolean	"active": true, "admin": false	Literal lowercase true or false
Null	"metadata": null	Literal lowercase null
Object	{"key": "value"}	Unordered collection of key/value pairs; keys must be double-quoted strings
Array	[1, 2, 3, "item"]	Ordered list of zero or more values separated by commas

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Common JSON Syntax Errors & Edge Cases

1. Trailing Commas: Commas after the final element in an array or object (e.g., {"a": 1,}) violate RFC 8259, causing standard parsers to throw errors.
2. Single Quotes: JSON forbids single quotes for keys or string values ({'key': 'val'} is invalid).
3. Unquoted Keys: JavaScript object syntax permits { key: "value" }, but JSON requires {"key": "value"}.
4. Number Overflow: JSON numbers with more than 53 bits of integer precision will lose precision in JavaScript runtimes unless handled as BigInt strings.

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Formatting and Validating JSON in Code

JavaScript

// Beautify JSON with 2-space indentation
function formatJsonString(rawJson, indentSpaces = 2) {
  try {
    const parsed = JSON.parse(rawJson);
    return { success: true, formatted: JSON.stringify(parsed, null, indentSpaces) };
  } catch (err) {
    return { success: false, error: err.message };
  }
}

// Minify JSON for production payload transfer
function minifyJsonString(rawJson) {
  const parsed = JSON.parse(rawJson);
  return JSON.stringify(parsed);
}

Python

import json

def prettify_json(raw_json_str: str) -> str:
    try:
        obj = json.loads(raw_json_str)
        return json.dumps(obj, indent=2, sort_keys=True)
    except json.JSONDecodeError as exc:
        return f"Invalid JSON: {exc}"