Fix Invalid JSON Online Free: Common Errors & Solutions

Got a JSON error? Paste it into our JSON Formatter to find the exact problem. Here are the most common JSON errors and how to fix them.

The 7 Most Common JSON Errors

1. Unexpected Token Error

This is the #1 JSON error developers encounter. It means the parser found a character it did not expect. The most common causes:

• Trailing commas: {"name": "John", "age": 30,} — the comma after 30 is invalid in JSON. Remove it.
• Single quotes: {'name': 'John'} — JSON requires double quotes. Change to {"name": "John"}.
• Unquoted keys: {name: "John"} — all keys must be in double quotes.
• Comments: {"name": "John" // user} — JSON does not support comments.

2. Unexpected End of JSON Input

Your JSON is incomplete. Missing a closing } or ]. Count your brackets — every opening bracket needs a matching close.

3. Expected Property Name or '}'

Usually a missing comma between key-value pairs:

// Wrong\n{"name": "John" "age": 30}\n// Correct\n{"name": "John", "age": 30}

4. Bad Escape Character

Backslashes in JSON strings must be escaped as \\. File paths like C:\Users\file must be C:\\Users\\file.

5. Duplicate Keys

While technically valid JSON, duplicate keys cause unpredictable behavior. The last value wins in most parsers.

6. Number Format Errors

Leading zeros (09), hex numbers (0xFF), and NaN/Infinity are not valid JSON numbers.

7. BOM (Byte Order Mark)

Some editors add an invisible BOM character at the start of the file. This causes "Unexpected token" at position 0. Remove it with a hex editor or use our JSON Formatter which handles this automatically.

How to Prevent JSON Errors

• Use a JSON Schema Validator to validate structure
• Use YAML for config files where you need comments
• Always use JSON.stringify() to generate JSON, never string concatenation
• Set your editor to use double quotes for JSON files

Related: JSON Best Practices, YAML vs JSON, JSON Formatter