Free Online JSON Validator
Instantly check whether your JSON is syntactically valid with our free online JSON validator.
Validation happens in real time as you type or paste — no button clicks required.
When errors are found, you get the exact line and column number plus a
plain-English explanation of what went wrong, so you can fix it fast.
How it works
- Paste or type your JSON into the input panel on the left
- The result panel shows Valid JSON ✓ in green or a detailed error in red
- When invalid, the error line is highlighted and an explanation is shown below
- Fix the error and see the result update immediately
Features
- Real-time validation — validates as you type with a 300ms debounce
- Exact error location — line and column numbers for every error
- Plain-English errors — "Trailing comma before closing brace on line 4" instead of cryptic parser messages
- Error line highlighting — the problematic line is highlighted in red in the output panel
- JSON stats — when valid, shows size, type, key count, and nesting depth
- 100% client-side — your data never leaves your browser
- Dark mode first — developer-friendly dark theme with light mode toggle
- Mobile responsive — works on phones and tablets
Common JSON Validation Errors
Trailing Commas
JSON does not allow trailing commas after the last element in an object or array:
{ "name": "Alice", "age": 28, } ← trailing comma is invalid
Single Quotes
JSON requires double quotes. Single quotes are invalid:
{ 'name': 'Alice' } ← must use: { "name": "Alice" }
Unquoted Keys
All property names must be in double quotes:
{ name: "Alice" } ← invalid: { "name": "Alice" }
Missing Commas
Each key-value pair must be separated by a comma:
{
"name": "Alice"
"age": 28 ← missing comma after "Alice"
}
Mismatched Brackets
Every { needs a matching } and every [ needs a matching ]:
{ "items": [1, 2, 3 } ← closing brace should be bracket ]
Frequently Asked Questions
Is my JSON data safe?
Yes. All validation runs entirely in your browser using JavaScript. Your data is never sent to any server. The tool works offline too.
What JSON spec does this validate against?
This tool validates against the JSON specification (RFC 8259) using the browser's native JSON.parse(). It catches all standard syntax errors including trailing commas, missing quotes, invalid values, and structural issues.
Can it validate JSON Schema?
This tool validates JSON syntax — whether the document is well-formed JSON. It does not validate against a JSON Schema (e.g., checking that a field is required or has a specific type). Use our
JSON Formatter for structural exploration.
What's the difference between a JSON validator and a JSON formatter?
A validator checks whether JSON is syntactically correct. A formatter takes valid JSON and makes it readable by adding indentation and line breaks. Our
JSON Formatter does both simultaneously.
What file size can this handle?
There's no enforced limit. The validator handles files up to several megabytes smoothly. Very large files (10MB+) may have brief validation delays.