How to Fix 'Unexpected Token' in JSON: Complete Guide (2026)

What Is the 'Unexpected Token' Error in JSON?

The SyntaxError: Unexpected token error means the JSON parser encountered a character it did not expect. JSON has strict syntax rules defined in RFC 8259 — any deviation throws this error immediately.

5 Common Causes

1. Trailing Commas

The most frequent cause. JSON does not allow a comma after the last item in an array or object.

// INVALID
{"name": "Alice", "age": 30,}

// VALID
{"name": "Alice", "age": 30}

2. Single Quotes

JSON requires double quotes for all strings and keys. Single quotes are valid JavaScript but invalid JSON.

// INVALID
{'name': 'Alice'}

// VALID
{"name": "Alice"}

3. Unquoted Keys

// INVALID
{name: "Alice"}

// VALID
{"name": "Alice"}

4. Comments

JSON does not support // or /* */ comments. Remove them before parsing.

5. undefined, NaN, or Infinity

These JavaScript-only values are not valid in JSON. Replace with null or a number.

How to Fix It Fast

Paste your JSON into the JSON formatter at jsondecode.com — it highlights the exact error line and explains what went wrong.

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