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

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

# webdev# javascript# productivity# json
7 Common JSON Errors Developers Make (And How to Fix Them)Jsontoall tools

JSON is one of the most widely used data formats in modern software development. It is commonly used...

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 
}
Enter fullscreen mode Exit fullscreen mode

The comma between "John" and "age" is missing.

Correct JSON

{ 
"name": "John", 
"age": 30 
}
Enter fullscreen mode Exit fullscreen mode

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'
}
Enter fullscreen mode Exit fullscreen mode

This may work in JavaScript objects but not in JSON.

Correct JSON

{ 
"name": "John" 
}
Enter fullscreen mode Exit fullscreen mode

JSON parsers expect double quotes.

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

Invalid JSON

{ 
"name": "John", 
"age": 30, 
}
Enter fullscreen mode Exit fullscreen mode

The comma after the last property makes the JSON invalid.

Correct JSON

{ "name": "John", "age": 30 }
Enter fullscreen mode Exit fullscreen mode

Always remove the trailing comma.

4. Unescaped Characters
Certain characters inside JSON strings must be escaped properly.

Invalid JSON

{ 
"message": "He said "Hello"" 
}
Enter fullscreen mode Exit fullscreen mode

The quotes inside the string break the structure.

Correct JSON

{ 
"message": "He said \"Hello\"" 
}
Enter fullscreen mode Exit fullscreen mode

Special characters such as quotes and backslashes must be escaped.

5. Unsupported Data Types

  • string

  • number

  • boolean

  • object

  • array

  • null

Developers sometimes try to use unsupported values.

Invalid JSON

{ 
"createdAt": new Date() 
}
Enter fullscreen mode Exit fullscreen mode

JSON cannot store functions or constructors.

Correct JSON

{
  "createdAt": "2026-03-12T10:00:00Z"
}
Enter fullscreen mode Exit fullscreen mode

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 ] 
}
Enter fullscreen mode Exit fullscreen mode

The closing brackets do not match.

Correct JSON

{ "users": 
   [ { 
        "name": "John", 
        "age": 30 
} ] }
Enter fullscreen mode Exit fullscreen mode

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 always a good idea to validate and format it.

You can quickly check and validate JSON using an online validator:

This helps identify syntax errors instantly.

Quick Tips to Avoid JSON Errors

  • Here are some best practices that help prevent JSON mistakes:

  • 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

If you frequently work with JSON, these tools can help simplify your workflow.

• JSON Formatter
https://jsontoall.tools/json-formatter

• JSON Validator
https://jsontoall.tools/json-validator

• JSON Diff Tool
https://jsontoall.tools/json-diff

• JSON to CSV Converter
https://jsontoall.tools/json-to-csv

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.

What is the most confusing JSON error you have encountered while developing? Share your experience in the comments.