Common JSON Errors and How to Fix Them

Common JSON Errors

JSON syntax errors are easy to make but also easy to fix once you know what to look for.

Error 1: Missing or Extra Commas

Wrong

{
  "name": "John"
  "age": 30
}

{
  "name": "John",
  "age": 30,
}

Correct

{
  "name": "John",
  "age": 30
}

Error 2: Wrong Quote Characters

Wrong

{
  'name': 'John'
}

Correct

{
  "name": "John"
}

Always use double quotes in JSON!

Error 3: Unquoted Property Names

Wrong

{
  name: "John"
}

Correct

{
  "name": "John"
}

Error 4: Unescaped Special Characters

Wrong

{
  "message": "He said "Hello""
}

Correct

{
  "message": "He said \"Hello\""
}

Escape Sequences

• \" for quotes
• \\ for backslash
• \n for newline
• \t for tab

Error 5: Invalid Values

Wrong

{
  "value": undefined,
  "result": NaN,
  "status": active
}

Correct

{
  "value": null,
  "result": null,
  "status": "active"
}

Valid JSON values: string, number, boolean, null, array, object

Error 6: Incorrect Casing

Wrong

{
  "active": True,
  "data": NULL
}

Correct

{
  "active": true,
  "data": null
}

Always lowercase: true, false, null

Error 7: Mismatched Brackets

Wrong

{
  "items": [
    {"name": "Item 1"}
}

Correct

{
  "items": [
    {"name": "Item 1"}
  ]
}

Error 8: Comments in JSON

Wrong

{
  // This is a comment
  "name": "John"
}

Correct

{
  "name": "John"
}

Standard JSON doesn't support comments!

Debugging Tools

Online Validators

Big JSON Viewer - Shows exact error location

JSONLint - Classic validator

VS Code - Real-time validation

Command Line

# Python
python -m json.tool file.json

# jq
jq '.' file.json

Error Messages Decoded

| Error | Likely Cause |

|-------|--------------|

| "Unexpected token" | Wrong quotes, commas, brackets |

| "Unexpected end" | Missing closing bracket |

| "Expected property name" | Unquoted key or trailing comma |

Prevention Tips

Use JSON-aware editor (VS Code)

Enable auto-formatting

Validate before use

Use JSON.stringify() instead of manual construction

Advanced Debugging

Find Error Location

try {
  JSON.parse(jsonString);
} catch (e) {
  console.error('Error at position:', e.message);
}

Python Detailed Errors

import json

try:
    data = json.loads(json_string)
except json.JSONDecodeError as e:
    print(f"Error: {e.msg}")
    print(f"Line {e.lineno}, Column {e.colno}")

Conclusion

Most JSON errors are syntax issues. Use validation tools like Big JSON Viewer to quickly identify and fix problems!