7 Common JSON Errors Developers Make (And How to Fix Them)

Source: Dev.to

JSON is one of the most widely used data formats in modern software development. It is commonly used for APIs, configuration files, data storage, and communication between services.

Although JSON looks simple, small syntax mistakes can easily break an API request or crash an application. Many developers lose time debugging JSON issues that could have been avoided with simple validation.

In this article, we will explore 7 common JSON mistakes developers make and how to fix them quickly.

1. Missing Commas Between Properties

One of the most common JSON errors is forgetting a comma between key‑value pairs.

Invalid JSON

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

Correct JSON

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

Always make sure properties are separated by commas.

2. Using Single Quotes Instead of Double Quotes

JSON strictly requires double quotes for keys and string values.

Invalid JSON

{ 
  'name': 'John'
}

Correct JSON

{ 
  "name": "John" 
}

JSON parsers expect double quotes.

3. Trailing Commas

Trailing commas are allowed in JavaScript objects but not in JSON.

Invalid JSON

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

Correct JSON

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

Always remove the trailing comma.

4. Unescaped Characters

Certain characters inside JSON strings must be escaped properly.

Invalid JSON

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

Correct JSON

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

Special characters such as quotes and backslashes must be escaped.

5. Unsupported Data Types

JSON supports only the following data types:

• string
• number
• boolean
• object
• array
• null

Developers sometimes try to use unsupported values.

Invalid JSON

{ 
  "createdAt": new Date() 
}

Correct JSON

{
  "createdAt": "2026-03-12T10:00:00Z"
}

Dates should be stored as strings.

6. Improperly Nested Objects or Arrays

Incorrect nesting of objects or arrays can break JSON completely.

Invalid JSON

{ 
  "users": 
    [ { "name": "John", "age": 30 ] 
}

Correct JSON

{ 
  "users": [
    { 
      "name": "John", 
      "age": 30 
    } 
  ] 
}

Always verify that brackets {} and [] are properly balanced.

7. Forgetting to Validate JSON

One of the biggest mistakes developers make is not validating JSON before using it in APIs or applications. Even a small syntax error can cause an API request to fail.

Before sending JSON data, it is a good idea to validate and format it. You can quickly check and validate JSON using an online validator:

JSON Validator

Quick Tips to Avoid JSON Errors

• Always validate JSON before using it in APIs.
• Use JSON formatters to visualize complex structures.
• Avoid trailing commas.
• Always use double quotes for keys and string values.
• Check bracket balance when nesting objects and arrays.

Useful JSON Tools for Developers

• JSON Formatter
• JSON Validator
• JSON Diff Tool
• JSON to CSV Converter

These tools can help developers debug, validate, and transform JSON data much faster.

Final Thoughts

JSON is simple but strict. Small syntax mistakes can easily break APIs or applications if not handled properly. Understanding these common JSON errors will help you debug problems faster and write more reliable code.

If you regularly work with APIs or configuration files, keeping a few JSON tools handy can save a lot of time.