Debugging JSON: Common Issues and How to Fix Them

JSON errors are among the most common bugs in web development. This guide covers the issues you'll encounter most often and how to fix them quickly.

Top 10 JSON Errors

1. Trailing Commas

{

  "name": "Alice",  ← Remove this comma
}

Fix: Remove trailing commas after the last property.

2. Single Quotes

{'name': 'Alice'}  ← Wrong

Fix: Always use double quotes for strings and keys.

3. Unquoted Keys

{name: "Alice"}  ← Wrong

Fix: All keys must be in double quotes: {"name": "Alice"}

4. Comments in JSON

{

  // This is not valid JSON
  "name": "Alice"
}

Fix: JSON doesn't support comments. Remove them or use JSONC format.

5. Special Characters in Strings

{"text": "Line 1

Line 2"}  ← Newlines must be escaped

Fix: Use \n for newlines: "Line 1\nLine 2"

6. Undefined and NaN Values

{"value": undefined}  ← Not valid JSON

Fix: Use null instead: {"value": null}

7. Hex Numbers

{"color": 0xFF0000}  ← Not valid JSON

Fix: Use strings for hex: {"color": "#FF0000"}

8. Incorrect Nesting

{"users": {"name": "Alice"},}  ← Extra brace

Fix: Match all opening and closing brackets carefully.

9. Unicode Issues

{"emoji": "🎉"}  ← Usually works, but escape if needed

10. BOM Characters

Files saved with BOM can cause parse errors. Fix: Save as UTF-8 without BOM.

Debugging Workflow

Prevention Tips