Common JSON Errors and How to Fix Them

July 12, 2026 4 min read

1. Trailing Commas

The most common mistake. JavaScript allows trailing commas in objects and arrays, but JSON does not:

// ❌ Invalid — trailing comma
{ "name": "Alice", "age": 30, }

// ✅ Valid
{ "name": "Alice", "age": 30 }

JSON requires double quotes for all string values and keys. Single quotes will cause a parse error:

// ❌ Invalid
{ 'name': 'Alice' }

// ✅ Valid
{ "name": "Alice" }

Keys must always be quoted strings. This is not JavaScript — you cannot omit quotes on property names:

// ❌ Invalid
{ name: "Alice" }

// ✅ Valid
{ "name": "Alice" }

JSON does not support comments. Remove all // and /* */ blocks before parsing:

// ❌ Invalid
{
  // This is a comment
  "name": "Alice"
}

// ✅ Valid
{
  "name": "Alice"
}

Every opening { or [ must have a matching closing pair. A missing bracket is the second most common cause of parse errors:

// ❌ Invalid — missing closing brace
{ "users": [ { "id": 1 } ]

// ✅ Valid
{ "users": [ { "id": 1 } ] }

Quick fix: Paste your JSON into a formatter. It will highlight the exact location of mismatched brackets.

JSON must have exactly one root value. Extra data after the closing brace causes a parse error:

// ❌ Invalid
{"name": "Alice"} {"age": 30}

// ✅ Valid
{"name": "Alice", "age": 30}

Validate and fix your JSON instantly?