Free JSON Formatter & Validator
Paste your JSON below to instantly format, prettify, and validate it. Everything runs in your browser — your data is never sent to a server.
About This JSON Formatter
🔒 100% Private
All processing happens in your browser using JavaScript. No JSON is ever uploaded to a server. Safe for sensitive data.
✏ Syntax Validation
Displays clear error messages with the line and character position when your JSON has syntax errors. Fix issues fast.
📋 Easy Copy
One-click copy to clipboard. Supports formatted output with 2-space, 4-space, or tab indentation.
⚡ Instant
No page reload, no server round-trip. Format multi-megabyte JSON files in milliseconds.
How to Use the JSON Formatter
- Paste your JSON into the input box on the left (or click Load Sample to try a demo)
- Select your preferred indentation (2 spaces, 4 spaces, or tabs)
- Click Format / Validate to prettify your JSON and check for errors
- If errors exist, a red error message will show the exact location
- Click Copy Output to copy the formatted JSON to your clipboard
- Use Minify to compress JSON by removing all whitespace
What is JSON?
JSON (JavaScript Object Notation) is a lightweight, human-readable data interchange format. It's the standard way web APIs exchange data and how many configuration files are written. JSON represents data as key-value pairs, arrays, strings, numbers, booleans, and null values.
A well-formed JSON document either starts with { (an object) or [ (an array). Common JSON errors include trailing commas, single quotes instead of double quotes, unquoted keys, and missing commas between elements.
Common JSON Errors and How to Fix Them
| Error | Example (Bad) | Fixed |
|---|---|---|
| Trailing comma | {"a": 1,} | {"a": 1} |
| Single quotes | {'name': 'Alice'} | {"name": "Alice"} |
| Unquoted key | {name: "Alice"} | {"name": "Alice"} |
| Missing comma | {"a":1 "b":2} | {"a":1,"b":2} |
| Comments | { // comment } | Remove comments |
Frequently Asked Questions
Is this JSON formatter safe to use with sensitive data?
Yes. All processing is done entirely in your browser using JavaScript. Your JSON is never sent to any server. You can verify this by opening your browser's Network tab in DevTools — you'll see no requests made when you format JSON.
What is the maximum file size this tool can handle?
There's no hard limit — it depends on your browser's available memory. In practice, most browsers can handle JSON files up to 50MB without issues. For very large files (100MB+), consider using a command-line tool like jq instead.
What is the difference between formatting and minifying JSON?
Formatting (prettifying) adds indentation and newlines to make JSON human-readable. Minifying removes all unnecessary whitespace to produce the smallest possible file size — useful when sending JSON over a network API to reduce bandwidth.
Why does my JSON fail validation with comments?
Standard JSON (per RFC 8259) does not support comments. If you have a JSON file with // or /* */ comments, it's technically JSONC (JSON with Comments), which is used by some configuration files (tsconfig.json, .vscode/settings.json). You'll need to remove comments before it validates as standard JSON.