JSON Parse Errors: How to Fix Every Common Syntax Error

JSON Parse Errors: Every Error Explained and Fixed

JSON parse errors are some of the most common errors in web development. Whether you are calling an API, reading a config file, or debugging a data pipeline, invalid JSON stops everything. This guide covers every common JSON syntax error with the exact fix for each one.

How to Read a JSON Parse Error

When JSON.parse() fails in JavaScript, the error message tells you where the problem is:

SyntaxError: Unexpected token } in JSON at position 47

The position number is the character offset from the start of the string. Counting from zero by hand is painful. Paste the JSON into JSONKit's validator at /json-validator instead — it shows you the exact line number and column number and highlights the error in red.

Error 1: Trailing Comma

The most common JSON mistake. JavaScript allows trailing commas. JSON does not.

Bad:

{
  "name": "Ravi",
  "age": 28,
}

Fixed:

{
  "name": "Ravi",
  "age": 28
}

Remove the comma after the last property. The same rule applies to the last item in an array: `[1, 2, 3,]` is invalid JSON.

Error 2: Single Quotes

JavaScript objects use single quotes freely. JSON requires double quotes for every string — both keys and values.

Bad:

{'name': 'Ravi', 'city': 'Surat'}

Fixed:

{"name": "Ravi", "city": "Surat"}

Error 3: Unquoted Keys

JSON keys must always be strings wrapped in double quotes. JavaScript object syntax allows unquoted keys; JSON does not.

Bad:

{name: "Ravi", age: 28}

Fixed:

{"name": "Ravi", "age": 28}

Error 4: undefined, NaN, and Infinity

These are valid JavaScript values but are not part of the JSON specification. Use null instead.

Bad:

{"result": undefined, "ratio": NaN, "limit": Infinity}

Fixed:

{"result": null, "ratio": null, "limit": null}

Note: JSON.stringify() in JavaScript silently converts NaN and Infinity to null and drops undefined properties entirely.

Error 5: Comments

JSON does not support comments of any kind — no // single-line comments and no /* */ block comments.

Bad:

{
  // database config
  "host": "localhost",
  "port": 5432 /* default postgres port */
}

Fixed: remove all comments. If you need commented config files, use YAML instead — it supports # comments natively.

Error 6: Missing Comma Between Properties

Each property in a JSON object must be separated by a comma.

Bad:

{
  "name": "Ravi"
  "age": 28
}

Fixed:

{
  "name": "Ravi",
  "age": 28
}

The parser hits the unexpected `"` at the start of `"age"` and throws because it expected either `,` or `}`.

Error 7: Missing Closing Bracket or Brace

Every opening bracket `[` or brace `{` must have a matching closing bracket `]` or `}`.

Bad:

{"users": [{"name": "Ravi"}, {"name": "Priya"}

Fixed:

{"users": [{"name": "Ravi"}, {"name": "Priya"}]}

For large JSON files, use JSONKit's formatter — it will immediately show you where the brackets are unbalanced.

Error 8: Number as Key

JSON object keys must always be strings. A number as a key is invalid.

Bad:

{1: "one", 2: "two"}

Fixed:

{"1": "one", "2": "two"}

Error 9: Extra Data After the Root Value

JSON allows exactly one root value. Any text after the closing brace or bracket causes a parse error.

This commonly happens when an API response returns two JSON objects instead of wrapping them in an array:

Bad:

{"id": 1}{"id": 2}

Fixed:

[{"id": 1}, {"id": 2}]

Error 10: String with Unescaped Special Characters

Strings in JSON must not contain raw newlines, tabs, or backslashes — these must be escaped.

Bad:

{"path": "C:Users
avidocuments"}

Fixed:

{"path": "C:\Users\ravi\documents"}

Escape sequences in JSON: `\\` for backslash, `\n` for newline, `\t` for tab, `\"` for double quote.

How to Fix JSON Errors Fast

The fastest way to fix JSON errors is to paste your JSON into JSONKit's validator at /json-validator. It:

• Highlights the error with exact line and column numbers
• Explains what went wrong in plain English
• Updates live as you type — you see the error disappear the moment you fix it
• Shows a green success card with file size and line count once the JSON is valid

For programmatic validation in JavaScript or Python, wrap JSON.parse() or json.loads() in a try/catch block and log the error message.