JSON Validator Online
Paste JSON, get instant validation. The tool pinpoints the exact line and character where syntax breaks.
JSON Formatter
Use this tool directly in your browser — no signup required.
Use JSON Formatter100% private — files are processed locally and never uploaded.
How to JSON Validator Online
- 1
Paste the JSON you want to check
Paste JSON from any source — API response, config file, hand-written data, or a colleague's code.
- 2
Run validation
Click validate. The parser checks for strict JSON compliance and reports any errors with line numbers.
- 3
Fix the reported issues
Use the error messages to locate and fix problems. Common issues include trailing commas, single quotes, and unquoted keys.
JSON Parsing Errors Are Cryptic Without Help
"Unexpected token < at position 0" — that's what you get from JSON.parse() when something goes wrong. It tells you almost nothing. The actual problem might be a trailing comma on line 47, but the parser chokes at the first point where the syntax becomes ambiguous.
A proper validator does more than just say "invalid." It walks through the JSON structure, checks every bracket match, every quoted string, every comma placement, and reports the specific issue. "Expected comma or closing brace at line 23, column 15" — that's actionable.
Common mistakes that break JSON but look fine at a glance: trailing commas after the last item in an array or object (valid in JavaScript, invalid in JSON), single quotes instead of double quotes, unquoted property names, and comments (JSON doesn't allow them).
Frequently Asked Questions
What's the difference between JSON and JavaScript objects?
JSON is stricter. Keys must be double-quoted strings. No trailing commas. No comments. No single quotes. No undefined values. JavaScript objects allow all of those. Code that works in JS often fails as JSON.
Can I validate JSON with comments?
Standard JSON doesn't support comments. Some tools (like VS Code's jsonc mode) allow them, but they must be stripped before parsing as strict JSON. This validator checks against the official JSON spec.
Why does my API response fail validation?
Check that the response is actually JSON. APIs sometimes return HTML error pages, XML, or plain text when something goes wrong server-side. If the response starts with < or doesn't start with { or [, it's not JSON.