JSON Formatter & Validator — Free Online
Paste raw or minified JSON to instantly format, validate, and syntax-highlight it. Find errors immediately. Runs entirely in your browser.
What This Tool Does
The JSON Formatter takes raw, minified, or malformed JSON text and reformats it with proper indentation, line breaks, and syntax highlighting. It also validates the JSON as you type — instantly flagging syntax errors with the line and character position.
This is an essential tool for developers working with APIs, configuration files, log files, or any system that outputs JSON data. Minified JSON is unreadable; this tool makes it instantly scannable.
How to Use the JSON Formatter
- Paste your JSON text into the input area, or drag-and-drop a .json file
- The formatter automatically validates and formats on paste or file drop
- Errors are highlighted with line numbers
- Click Copy to copy the formatted output
- Click Minify to compress back to a single line
Common JSON Errors This Tool Detects
| Error | Example | Fix |
|---|---|---|
| Trailing comma | {"a":1,} | Remove the last comma |
| Single quotes | {"a":'b'} | Replace with double quotes |
| Unquoted keys | {a:1} | Quote all keys: {"a":1} |
| Missing quotes | {"a":hello} | Quote string values: {"a":"hello"} |
| Unclosed brackets | {"a":[1,2 | Add missing ] and } |
| Comments | // comment | JSON does not support comments |
Why JSON Formatting Matters
JSON (JavaScript Object Notation) is the dominant data interchange format for web APIs, configuration files, and data storage. It is designed to be both human-readable and machine-parseable — but only when properly formatted.
Minified JSON removes all whitespace to reduce file size for transmission. This is ideal for sending data over a network, but completely unreadable for debugging or inspection. The formatter reverses this process.
- API debugging — understand the structure of API responses immediately
- Config file editing — find and fix errors in package.json, tsconfig.json, and similar files
- Log analysis — structured logs in JSON format become readable
- Data exploration — understand nested data structures visually
- Code review — share formatted JSON with colleagues for discussion
JSON Syntax Rules
JSON has strict syntax rules that differ from JavaScript object notation:
- All keys must be enclosed in double quotes
- String values must use double quotes, not single quotes
- No trailing commas after the last item in an object or array
- No comments are permitted in JSON
- Numbers must not have leading zeros (except for 0 itself)
- Special characters in strings must be escaped with a backslash
Privacy & Security
All JSON formatting and validation runs in your browser using JavaScript. No data is sent to any server. This is important when working with sensitive API keys, user data, or proprietary configuration files.
💡 Once your JSON is formatted, you may need to work with it in other tools. Use the JSON to CSV converter to flatten a JSON array into a spreadsheet, or the XML to JSON converter if your source data is XML. For validating the structure independently of formatting, try the JSON Validator.
Related Guides & Tutorials
JSON Workflow Tools
Formatting is just one step in working with JSON data:
- Validate JSON syntax — check for errors before formatting or sharing
- Convert JSON to CSV for analysis in Excel or Google Sheets
- Convert CSV to JSON to go the other direction
- Convert JSON to XML for systems that require XML format
- Decode JWT tokens — JWTs carry a JSON payload readable with this formatter
Frequently Asked Questions
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- Getting HTML back from an API? Use the HTML Formatter to beautify and read it. → format your HTML response bodies
- JSON payloads often contain Unix timestamps. Decode them instantly with the Timestamp Converter. → decode Unix timestamps in JSON