buildFix Guide

How to Fix Invalid JSON

Invalid JSON is frustrating — but every JSON syntax error has a clear pattern and a clear fix. This guide walks you through diagnosing the error, finding the line, and applying the right fix for every common case.

check_circleValidate My JSONerrorFull Error Reference

The 4-Step JSON Fix Process

1
content_paste

Paste into Validator

Copy your broken JSON and paste it into the JSON Validator to get the exact error message and line number.

2
search

Read the Error

The error message tells you what went wrong. "Unexpected token ," usually means trailing comma. "Unexpected end" means a missing bracket.

3
edit

Apply the Fix

Find your error type below and follow the step-by-step fix. Each section has an invalid/valid code pair.

4
check_circle

Re-validate

Paste the fixed JSON back into the validator. If there are multiple errors, fix them one at a time from the top.

Jump to Fix

Trailing CommaSingle Quotes Instead of Double QuotesUnquoted Object KeysComments in JSONundefined or NaN ValuesMissing or Extra BracketUnescaped Special Characters in Strings
error

Trailing Comma

Most Common
SyntaxError: Unexpected token }

cancel Invalid JSON

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

check_circle Fixed JSON

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

Fix Steps

  1. 1Find the last key-value pair before a closing } or ]
  2. 2Remove the comma after that last item
  3. 3Re-validate your JSON

Tip: Most text editors with JSON syntax highlighting will highlight trailing commas as errors.

error

Single Quotes Instead of Double Quotes

Very Common
SyntaxError: Unexpected token '

cancel Invalid JSON

{
  'name': 'Alice',
  'age': 30
}

check_circle Fixed JSON

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

Fix Steps

  1. 1Use Find & Replace to replace all ' with "
  2. 2Be careful not to replace apostrophes inside string values
  3. 3Validate the result

Tip: JSON requires double quotes everywhere. Single quotes are only valid in JavaScript, not JSON.

error

Unquoted Object Keys

Very Common
SyntaxError: Unexpected token n

cancel Invalid JSON

{
  name: "Alice",
  age: 30
}

check_circle Fixed JSON

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

Fix Steps

  1. 1Find all object keys (words before the : colon)
  2. 2Wrap each key in double quotes
  3. 3Validate the result

Tip: In JavaScript, object keys are optional to quote. In JSON, they are always required.

error

Comments in JSON

Common
SyntaxError: Unexpected token /

cancel Invalid JSON

{
  "name": "Alice" // the user
  // "age": 30
}

check_circle Fixed JSON

{
  "name": "Alice"
}

Fix Steps

  1. 1Remove all // line comments
  2. 2Remove all /* block comments */
  3. 3Remove commented-out keys entirely

Tip: JSON has no comment syntax by design. Use JSON5 or JSONC if you need comments during development.

error

undefined or NaN Values

Common
SyntaxError: Unexpected token u

cancel Invalid JSON

{
  "value": undefined,
  "score": NaN,
  "limit": Infinity
}

check_circle Fixed JSON

{
  "value": null,
  "score": null,
  "limit": null
}

Fix Steps

  1. 1Replace undefined with null
  2. 2Replace NaN with null or a valid number
  3. 3Replace Infinity with null or a large number

Tip: undefined, NaN, and Infinity are JavaScript values. JSON only supports null as a non-value.

error

Missing or Extra Bracket

Common
SyntaxError: Unexpected end of JSON input

cancel Invalid JSON

{
  "users": [
    {"name": "Alice"},
    {"name": "Bob"}

}

check_circle Fixed JSON

{
  "users": [
    {"name": "Alice"},
    {"name": "Bob"}
  ]
}

Fix Steps

  1. 1Count opening { and [ brackets
  2. 2Count closing } and ] brackets — they must match
  3. 3Add or remove brackets to balance them

Tip: Use a JSON formatter — it will visually indent the structure and make missing brackets obvious.

error

Unescaped Special Characters in Strings

Less Common
SyntaxError: Bad control character in string literal

cancel Invalid JSON

{
  "message": "line one
line two",
  "path": "C:UsersAlice"
}

check_circle Fixed JSON

{
  "message": "line one\nline two",
  "path": "C:\\Users\\Alice"
}

Fix Steps

  1. 1Replace actual newlines inside strings with \n
  2. 2Replace backslashes with \\
  3. 3Replace tabs with \t

Tip: Control characters and backslashes must be escaped inside JSON strings. Use JSON.stringify() to safely serialize values.

Still Stuck?

If you've applied the fix but still get a parse error, there may be multiple errors in your JSON. Parsers typically report only the first error they encounter. Fix errors one at a time from the top of the file, re-validating after each fix.

For complex or large JSON, try the JSON Formatter — it will attempt to pretty-print your JSON and may make structural problems visually obvious. The JSON Viewer shows JSON as a collapsible tree which makes missing brackets easy to spot.

If you want to understand why each of these fixes is required, not just how to apply it, see the JSON Syntax reference for the underlying RFC 8259 grammar.

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FAQ – Fixing Invalid JSON

How do I fix a JSON syntax error?expand_more

Paste your JSON into a JSON validator to get the exact error message and line number. Then fix the specific problem — common fixes include removing trailing commas, replacing single quotes with double quotes, quoting object keys, and removing comments.

How do I find invalid JSON in a large file?expand_more

Use a JSON validator or formatter tool — it will pinpoint the exact line number of the first syntax error. For very large files, try splitting the JSON into smaller chunks to isolate the problem section.

Can I fix JSON automatically?expand_more

Some JSON formatters can auto-fix simple issues like trailing commas and whitespace. However, most syntax errors require manual fixes because the parser cannot guess your intent — for example, it cannot know whether a missing comma or a missing closing bracket is the real problem.

What does "Unexpected token" mean in a JSON error?expand_more

An "Unexpected token" error means the JSON parser encountered a character it didn't expect at that position. This is usually caused by a trailing comma, a single quote instead of a double quote, an unquoted key, or a comment inside the JSON.

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