How to Validate JSON and Fix Common Errors

Validating JSON is a common checkpoint for developers working with APIs, configurations, or database serialization. Unlike JavaScript, JSON syntax is strictly defined by the RFC 8259 specification. A single misplaced symbol can cause parsers to reject your data.

In this guide, we will analyze the most common JSON syntax errors and look at how to resolve them.

The JSON Specification Rules

JSON syntax rules are rigid:

• Object keys and string values must use double quotes (").
• Numeric values, booleans (true/false), and null are unquoted.
• Commas serve strictly as delimiters; trailing commas are prohibited.
• Curly braces {} represent objects, while square brackets [] represent arrays.

Common Syntax Errors & How to Fix Them

1. Trailing Commas

A trailing comma before a closing bracket is the most frequent cause of parse exceptions.

Invalid JSON:

{
  "name": "Jane",
  "status": "pending",
}

Valid JSON:

{
  "name": "Jane",
  "status": "pending"
}

2. Single Quotes

JavaScript allows single quotes for strings, but JSON forbids them entirely.

Invalid JSON:

{
  'username': 'developer_101'
}

Valid JSON:

{
  "username": "developer_101"
}

3. Missing Quotes on Keys

In JSON, every object key must be double-quoted.

Invalid JSON:

{
  port: 8080
}

Valid JSON:

{
  "port": 8080
}

Debugging Bracket Mismatches

For large JSON payloads, mismatched braces or brackets can be tough to debug. A good JSON validator parses your structure step-by-step and points you directly to the offending line number. When debugging, look for missing commas or unclosed arrays within large nested objects.