JSON Validator & Formatter | Validate and Format JSON Effortlessly

Use our JSON Validator & Formatter to check for syntax errors and improve readability. Enter JSON directly or upload a file for formatting.


Your formatted JSON will appear here.

Instructions & Features

How to Use

  1. Paste your JSON data in the input area or use the upload button
  2. Click "Validate & Format" to check and beautify your JSON
  3. Use "Minify" to compress the JSON by removing whitespace
  4. Copy or download the result, or open the tree view to browse it

Features

  • Validation with precise error line and column
  • Pretty-print with selectable indent (2, 4, or tab)
  • Minify to remove all unnecessary whitespace
  • Tree view, syntax highlighting, copy and download
  • File upload for .json and .txt, plus sample data

Private & In-Browser

Your JSON never leaves your device. All validation and formatting runs locally in your browser, so even large or sensitive payloads stay private.

  • Nothing is uploaded to any server
  • No data is logged or stored
  • Works offline once the page has loaded

Use this tool from your AI agent

Free JSON API and Model Context Protocol (MCP) server. No signup, no API key, CORS open. Designed for Claude, ChatGPT, Cursor, scripts and frontend apps. 

curl -X POST https://mate.tools/api/v1/json-format.php \
  -H "Content-Type: application/json" \
  -d '{"json":"{\"a\":1,\"b\":[1,2,3]}","mode":"pretty"}'
import urllib.request, json

req = urllib.request.Request(
    "https://mate.tools/api/v1/json-format.php",
    data=json.dumps({"json":"{\"a\":1,\"b\":[1,2,3]}","mode":"pretty"}).encode(),
    headers={"Content-Type": "application/json"},
)
with urllib.request.urlopen(req) as r:
    print(json.load(r))
const r = await fetch("https://mate.tools/api/v1/json-format.php", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({"json":"{\"a\":1,\"b\":[1,2,3]}","mode":"pretty"}),
});
console.log(await r.json());

Add to claude_desktop_config.json (Claude Desktop), ~/.cursor/mcp.json (Cursor), or any other MCP-compatible client: 

{
  "mcpServers": {
    "mate-tools": {
      "command": "npx",
      "args": ["-y", "@mate-tools/mcp-server"]
    }
  }
}
API documentation OpenAPI 3.1 npm 60 req/min · 600 req/hour · 1 MB body cap

Frequently Asked Questions

Common JSON syntax errors include: missing or extra commas, unquoted keys (JSON requires double quotes around all keys), single quotes instead of double quotes, trailing commas after the last item, and unescaped special characters in strings. The tool points to the exact line and column where parsing failed.

Formatting (beautifying) adds proper indentation and line breaks to make JSON human-readable. Minifying removes all unnecessary whitespace to reduce file size, which is useful for production environments and API responses.

Yes, you can upload .json or .txt files using the upload button. The tool reads the file content and validates it. You can also paste JSON directly or load the sample data to try the tool.

Completely. This tool runs entirely in your browser using JavaScript. Your JSON is never uploaded, logged, or sent to any server, so even large or confidential data stays on your device.

Use the indent selector to pick 2 spaces, 4 spaces, or a tab character before clicking "Validate & Format". The formatted output and the copy/download buttons all use your chosen indentation.

What Is a JSON Validator & Formatter?

A JSON validator & formatter checks that your JSON is valid and, if so, neatly indents it for easy reading — or minifies it to save space. If there is an error, it points to the exact line and column where the problem is. Everything runs in your browser, so your data stays private.