JSON Validator

The most common JSON errors

These six cause nearly every “invalid JSON” error. The message under each one is exactly what the validator reports, and the fix is what the Repair button produces.

Trailing comma

JavaScript allows a comma after the last item; JSON does not.

{
  "name": "Ada",
  "admin": true,
}

Line 4, column 1: Trailing comma before } is not allowed

{
  "name": "Ada",
  "admin": true
}

Single quotes

Strings and keys must use double quotes.

{
  'name': 'Ada'
}

Line 2, column 3: Property names must be double-quoted strings

{
  "name": "Ada"
}

Unquoted key

Every key must be a double-quoted string, even simple ones.

{
  name: "Ada"
}

Line 2, column 3: Property names must be double-quoted strings

{
  "name": "Ada"
}

Comments

JSON has no comment syntax. Use JSONC or JSON5 files for configs that need comments.

{
  // the user name
  "name": "Ada"
}

Line 2, column 3: Property names must be double-quoted strings

{
  "name": "Ada"
}

Missing comma

Usually caused by adding a line without a comma on the line above.

{
  "name": "Ada"
  "admin": true
}

Line 3, column 3: Expected ',' or '}' after property value, found '"'

{
  "name": "Ada",
  "admin": true
}

Python values

Python’s print() output isn’t JSON. Use json.dumps() instead.

{
  "admin": True,
  "manager": None
}

Line 2, column 12: Unexpected 'T': expected a value

{
  "admin": true,
  "manager": null
}

Other things that are not valid JSON

• undefined, NaN and Infinity. Use null or a string.
• Numbers with leading zeros (007), a leading +, or hex like 0xFF.
• Raw line breaks or tabs inside strings. They must be written as \n and \t.
• Escapes other than \" \\ \/ \b \f \n \r \t \uXXXX. \' and \x41 are invalid.

Valid doesn’t always mean safe to parse. Repeated keys and numbers like 9007199254740993 or 1e400 are legal JSON, but JavaScript’s JSON.parse drops or changes them. The validator warns about both; see exactly what changes.

Validate JSON in code

function isValidJson(text) {
  try {
    JSON.parse(text);
    return true;
  } catch {
    return false;
  }
}

import json

try:
    json.loads(text)
except json.JSONDecodeError as e:
    print(f"line {e.lineno}, column {e.colno}: {e.msg}")

jq empty data.json && echo valid

Validating YAML instead? Use the YAML validator. Once your JSON is valid, the JSON formatter can pretty-print or sort it.

Frequently asked questions