JSON Formatter & Validator
Format, validate, and beautify JSON data instantly. Free online JSON formatter with syntax highlighting.
A JSON formatter that validates structure while pretty-printing, so you instantly see when a trailing comma, unquoted key, or unescaped character breaks your payload. Built for the messy reality of API work: paste a response, get a readable tree with 2-space indentation, and a pointer to the exact line that failed to parse. Nothing leaves your browser — parsing runs locally via the native JSON.parse engine.
JSON looks simple until you hit edge cases. Single quotes instead of double quotes, comments (not legal in spec-compliant JSON), trailing commas, NaN or Infinity, duplicate keys — any of these will crash a real parser but look fine in an editor. This tool catches them and tells you exactly where.
The formatter defaults to two-space indentation, which is the convention for most modern APIs, package.json, and tsconfig.json. Indented output preserves the exact data — numbers aren't silently coerced, Unicode escapes are kept as-is, and key order is maintained so diffs stay clean.
Most people use this while debugging an API response, validating a config file before deploying, or expanding a single-line JSON log entry into something a human can read.
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Paste your JSON
Drop any JSON string into the input area — an API response, a config file, a log line, or pasted output from curl. Minified and pretty-printed inputs both work.
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Review the formatted output
Valid JSON is pretty-printed with 2-space indentation. Invalid JSON shows a precise error pointing to the line and column where parsing failed, so you can fix the exact character.
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Copy or download
Copy to clipboard for quick use, or download as a .json file. The output is byte-faithful to the parsed input — no lossy conversion.
API response debugging
Paste a webhook or REST response to spot malformed fields before digging into your client code.
Config file validation
Validate package.json, tsconfig.json, or any JSON-based config before committing or shipping a deploy.
Log-line expansion
Many services log events as single-line JSON. Paste a line to expand it into something readable.
Infrastructure-as-code review
Check CloudFormation templates or Terraform's JSON output before handing them to the CLI.
Is my JSON data sent anywhere?
No. Parsing runs entirely in your browser using the native JSON.parse engine. Your data never leaves your device and isn't logged.
Why does my JSON fail even though it looks correct?
The usual suspects are single quotes instead of double quotes, trailing commas after the last item in an array or object, unquoted object keys, or JavaScript-style comments (// or /* */). The JSON spec forbids all of these. The error message points to the exact line.
Can it handle large JSON files?
Browsers typically handle 50–100 MB before performance degrades. For multi-gigabyte JSON, use a streaming parser like jq on the command line.
Does it support JSON5 or JSONC?
No. This tool validates strict RFC 8259 JSON. JSON5 features like comments, trailing commas, and unquoted keys will be flagged as errors. That's intentional — it surfaces issues before they hit a real parser.
What about very large numbers?
JavaScript's Number type loses precision above 2^53. If your JSON contains BigInt-range integers (like IDs from some databases), the parser will still display them, but be aware your downstream code may round them unless it handles strings.