Common JSON Validation Mistakes Developers Make and How to Fix Them

JSON (JavaScript Object Notation) is the universal data exchange format of the internet. However, despite its structural simplicity, JSON enforces a strict, unforgiving specification (RFC 8259) that differs sharply from standard JavaScript or TypeScript object literals.

A single extra comma or invalid quote mark can cause JSON.parse() to throw a fatal error and break API integrations.

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The Most Common JSON Errors & Solutions

1. Trailing Commas

Unlike JavaScript objects or arrays, JSON strictly forbids trailing commas after the last item.

// ❌ WRONG (Throws SyntaxError)
{
  "name": "DigitalMix",
  "category": "Tools",
}

// ✅ CORRECT
{
  "name": "DigitalMix",
  "category": "Tools"
}

2. Single Quotes instead of Double Quotes

JSON mandates double quotes (") around key names and string values. Single quotes (') or unquoted key identifiers are invalid.

// ❌ WRONG
{
  'id': 101,
  'role': 'admin'
}

// ✅ CORRECT
{
  "id": 101,
  "role": "admin"
}

3. Unescaped Control Characters in Strings

Newlines, tabs, and backslashes inside string values must be properly escaped.

// ❌ WRONG (Raw newline in string)
{
  "notes": "Line 1
Line 2"
}

// ✅ CORRECT
{
  "notes": "Line 1
Line 2"
}

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