JSON Formatter / Validator
Paste JSON and instantly format, validate, and inspect it — all in your browser.
Related Tools
What is a JSON Formatter?
A JSON formatter takes raw or minified JSON text and adds proper indentation, line breaks, and spacing to make it easy for humans to read. JSON (JavaScript Object Notation) is the universal data interchange format for APIs, configuration files, and AI-generated structured output — but unformatted JSON is nearly impossible to read at a glance.
JSON Kit's formatter runs entirely in your browser. There's no server, no upload, no data retention. Paste your payload, get instant results. The Monaco Editor (the same editor used in VS Code) powers both input and output panels, giving you syntax highlighting, error squiggles, and keyboard shortcuts you already know.
How to Use the JSON Formatter
- Paste your JSON string into the Input panel on the left.
- The Output panel on the right updates automatically as you type.
- Choose your indent style: 2 spaces (default), 4 spaces, or tabs.
- Click Minify to strip all whitespace for compact output.
- Use the Copy, Download, or Share buttons to export the result.
Code Examples
Input (minified):
{"user":{"id":1,"name":"Alice","roles":["admin","editor"]}}Output (formatted, 2 spaces):
{
"user": {
"id": 1,
"name": "Alice",
"roles": [
"admin",
"editor"
]
}
}Frequently Asked Questions
- What is JSON formatting?
- JSON formatting (also called JSON beautifying or pretty-printing) takes a compact or malformed JSON string and adds proper indentation and line breaks to make it human-readable. It doesn't change the data — only its visual structure. This is essential when debugging API responses, reading LLM outputs, or reviewing configuration files.
- Is my JSON data sent to any server?
- No. JSON Kit processes everything 100% in your browser using JavaScript. Your data never leaves your device. This is especially important when working with sensitive payloads like API keys, user data, or proprietary schemas.
- What's the difference between formatting and validating JSON?
- Formatting only changes whitespace — it beautifies or minifies the JSON. Validation checks whether the JSON is syntactically correct (proper quotes, no trailing commas, balanced brackets). JSON Kit does both: if your input has a syntax error, it highlights it with a red indicator and shows the exact error message.
- Why does my JSON have an 'Unexpected token' error?
- The most common causes are: (1) trailing commas after the last property or array element — not allowed in standard JSON, (2) single quotes instead of double quotes, (3) unquoted property keys, (4) comments (// or /* */) — JSON doesn't support comments. If your JSON came from an LLM or AI tool, try the Fix LLM JSON tool which repairs these issues automatically.
- What indentation should I use: 2 spaces, 4 spaces, or tabs?
- 2 spaces is the most common choice for JSON in JavaScript/TypeScript projects and is the default in most formatters. 4 spaces aligns with Python PEP 8 convention and is common in Python APIs. Tabs are preferred in some Go and Rust codebases. For machine consumption (sending JSON over HTTP), use minification — all whitespace is stripped.
- Can I format very large JSON files?
- Yes. JSON Kit uses the Monaco Editor (the same editor powering VS Code) which handles large files efficiently. Files up to ~50MB typically format without issues. For files over 50MB, consider using the command line: `cat large.json | python3 -m json.tool` or `jq . large.json`.
- What is JSON minification?
- Minification removes all unnecessary whitespace from JSON, reducing file size. A 10KB formatted JSON might compress to 6KB minified. This matters for: (1) HTTP API responses where bandwidth costs money, (2) localStorage limits in browsers, (3) embedding JSON in source code. Toggle the 'Minify' option to strip all formatting.
- How do I format JSON from the command line?
- You have several options: `jq . file.json` (requires jq), `python3 -m json.tool file.json`, `cat file.json | node -e "process.stdout.write(JSON.stringify(JSON.parse(require('fs').readFileSync('/dev/stdin','utf8')),null,2))"`. For piping: `curl api.example.com/endpoint | jq .`
About This Tool
JSON Kit's JSON Formatter is built for the AI era of development — where JSON constantly flows between LLMs, APIs, and vibe-coded apps. Unlike older formatters that send your data to a server, every operation here is client-side only. The tool handles files up to 50MB+, works on mobile, and is fully keyboard accessible. It's one of 40+ JSON tools in JSON Kit, all free, all browser-side.