Validating JSON — JSON Guide

10 Validating JSON

JSON is strict. A single misplaced comma or missing quote makes the entire file invalid. Validation checks that your JSON follows the rules.

Common Validation Errors

Error	What it means	Fix
`Unexpected token`	A character was found where it wasn't expected	Check for stray commas, extra brackets, or unquoted strings
`Expected ',' or '}'`	A comma or closing brace is missing	Add the missing comma or brace
`Expected '"'`	A string is missing its opening or closing quote	Add double quotes around the key or string value
`Unexpected number`	A number appeared where it isn't valid	Check for leading zeros or misplaced periods
`Trailing comma`	A comma after the last element in an object/array	Remove the comma after the last item

How to Validate JSON

Option 1 — Online validators: Paste your JSON into websites like jsonlint.com or jsonformatter.org. They highlight errors instantly.

Option 2 — Code editors: VS Code, Sublime Text, and others highlight JSON errors automatically. Look for red squiggly lines.

Option 3 — Command line: Use tools like jq or language-specific parsers:

# Using jq (Linux/macOS)
jq . file.json

# Using Python
python -m json.tool file.json

# Using Node.js
node -e "JSON.parse(require('fs').readFileSync('file.json','utf8'))"

Example: Fixing Invalid JSON

Invalid:

{
    "name": "Alice",
    age: 30,            // key not in double quotes
    "hobbies": ["art"]  // valid
}

Valid:

{
    "name": "Alice",
    "age": 30,          // added double quotes
    "hobbies": ["art"]
}

Pretty-Printing

Minified JSON is hard to read. Use pretty-printing to format it with indentation:

// Python
print(json.dumps(data, indent=2))

// JavaScript
JSON.stringify(data, null, 2)

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