5 Most Common JSON Errors (and How to Fix Them)

By JSONValidator.dev Team • 2025-07-04

Introduction: Why JSON Errors Are So Common

JSON is one of the most popular data formats for APIs, configuration, and data interchange. However, even small mistakes in your JSON can break apps, stop integrations, or make debugging a nightmare. Here are the five most common JSON errors (with real examples) and how to fix them.

1. Trailing Comma

In JSON, a comma is not allowed after the last item in an object or array. This is a common mistake when editing by hand.

Before:
{
  "name": "Alice",
  "age": 30,
}
After:
{
  "name": "Alice",
  "age": 30
}
Tip: Many code editors (and our online JSON tools) will highlight or automatically fix trailing commas.

2. Single vs. Double Quotes

JSON requires that all keys and string values use double quotes only. Single quotes are not valid.

Before:
{
  'name': 'Bob'
}
After:
{
  "name": "Bob"
}
Don't use single quotes—even if your programming language allows them! JSON syntax is stricter than JavaScript or Python.

3. Unescaped Characters

Certain characters (like newlines, tabs, or quotes inside a string) must be properly escaped with a backslash.

Before:
{
  "note": "This will break: "hello""
}
After:
{
  "note": "This will work: \"hello\""
}
If you see 'unexpected token' or 'unterminated string', check for missing escapes in your data.

4. Missing Brackets or Braces

Every opening bracket or brace must be matched by a closing one. A missing or extra bracket will always cause invalid JSON.

Before:
{
  "name": "Eve",
  "items": [1, 2, 3
}
After:
{
  "name": "Eve",
  "items": [1, 2, 3]
}
Use an online JSON validator to spot missing or extra brackets instantly.

5. Data Type Errors

Numbers, booleans, and null should not be wrapped in quotes. For example, 42 is valid, but "42" is a string, not a number.

  • "true" (string) is not the same as true (boolean)
  • "null" (string) is not the same as null (value)
  • "42" (string) is not the same as 42 (number)
Before:
{
  "age": "42",
  "active": "true"
}
After:
{
  "age": 42,
  "active": true
}

How Our Tool Can Help

Paste your JSON into our validator or repair tool to spot and fix these errors instantly. Our tools will point out the exact problem—and even suggest automatic repairs for many common issues.