5 Common JSON Errors and How to Fix Them

We've all been there: you paste a massive JSON blob into your code, and everything crashes. Here are the top 5 syntax errors developers make with JSON. Use our JSON Validator to catch these errors instantly.

1. Trailing Commas

The Mistake: { "a": 1, "b": 2, }

The Fix: JSON standard (RFC 8259) forbids commas after the last element. Remove it. This is one of the most common issues caught by our JSON validator tool.

2. Single Quotes Instead of Double Quotes

The Mistake: { 'key': 'value' }

The Fix: JSON must use double quotes ". Single quotes are valid in JavaScript, but not in JSON. Always use double quotes for both keys and values.

3. Unquoted Keys

The Mistake: { key: "value" }

The Fix: Always wrap your property names in double quotes: { "key": "value" }. Property names must be strings in valid JSON.

4. Comments in JSON

The Mistake: // This is a comment

The Fix: Standard JSON does not support comments. If you need configuration with comments, consider using YAML or JSON5 instead.

5. Undefined or Functions

The Mistake: Trying to serialize undefined or functions.

The Fix: JSON serves as a data interchange format. It only supports strings, numbers, booleans, null, arrays, and objects. Use JSON formatting tools to validate your data types.

Learn More About JSON

Want to understand JSON better? Check out our JSON Structure Guide or read about What is JSON for beginners.