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
}
The comma between "John" and "age" is missing.
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'
}
This may work in JavaScript objects but not in JSON.
Correct JSON
{
"name": "John"
}
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,
}
The comma after the last property makes the JSON invalid.
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""
}
The quotes inside the string break the structure.
Correct JSON
{
"message": "He said \"Hello\""
}
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()
}
JSON cannot store functions or constructors.
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 ]
}
The closing brackets do not match.
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 always a good idea to validate and format it.
You can quickly check and validate JSON using an online validator:
• JSON Validator
• 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.
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