10 Common JSON Errors and How to Fix Them (2026)

Why JSON Errors Matter

JSON errors can bring your application to a grinding halt. Whether you are consuming an API, reading a config file, or parsing user input, understanding common JSON errors saves hours of debugging time. Let us explore the most frequent mistakes and their solutions.

1. Trailing Commas

The most common JSON error is leaving a comma after the last element.

Wrong:

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

Right:

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

Fix: Remove trailing commas before the closing brace or bracket. Our JSON formatter automatically detects and highlights these errors.

2. Single Quotes Instead of Double Quotes

JSON requires double quotes for strings and keys.

Wrong:

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

Right:

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

Fix: Replace all single quotes with double quotes. Be careful with nested quotes in strings.

3. Unquoted Keys

Object keys must always be quoted in JSON.

Wrong:

{ name: "John", age: 30 }

Right:

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

Fix: Wrap all object keys in double quotes.

4. Undefined Values

JavaScript undefined is not valid in JSON.

Wrong:

{ "name": "John", "nickname": undefined }

Right:

{ "name": "John", "nickname": null }

Fix: Replace undefined with null or omit the property entirely.

5. Comments in JSON

Standard JSON does not support comments.

Wrong:

{ "name": "John" /* user name */ }

Right:

{ "name": "John" }

Fix: Remove comments or use JSON-C format if your parser supports it.

6. Malformed Unicode

Invalid escape sequences break JSON parsing.

Wrong:

{ "text": "Hello \xWorld" }

Right:

{ "text": "Hello \u0057orld" }

Fix: Use proper Unicode escape sequences (\uXXXX) or valid escape characters.

7. Unescaped Characters

Special characters must be escaped.

Wrong:

{ "text": "Line 1
Line 2" }

Right:

{ "text": "Line 1\nLine 2" }

Fix: Escape newlines (\n), tabs (\t), and quotes (") properly.

8. Circular References

Objects that reference themselves cannot be serialized.

Wrong:

const obj = {}; obj.self = obj; JSON.stringify(obj);

Right:

Remove circular references before serialization or use a replacer function.

Fix: Use a library like circular-json or implement custom serialization.

9. NaN and Infinity

JSON does not support special numeric values.

Wrong:

{ "value": NaN, "big": Infinity }

Right:

{ "value": null, "big": null }

Fix: Replace NaN and Infinity with null or use a custom JSON serializer.

10. Encoding Issues

UTF-8 is the standard encoding for JSON.

Problem: Files saved with BOM or Windows-1252 encoding. Solution: Ensure all JSON files are saved as UTF-8 without BOM.

Prevention Tips

• Use a JSON validator before deploying
• Enable strict mode in your JSON parser
• Write unit tests for JSON serialization
• Use TypeScript for compile-time type checking

Conclusion

Most JSON errors are preventable with proper tooling and awareness. Use our online JSON validator to catch errors before they reach production, and save yourself hours of debugging time.