Free online JSON Formatter & Validator. Prettify, validate, and inspect JSON payloads with 2/4 space indentation, instant syntax error markers, and minify tools. 100% private in-browser execution.
⚡ Interactive Calculation Engine Active
Please enable JavaScript in your browser to run live computations, 2D envelope diagrams, and export PDF reports.
How to Use JSON Formatter & Validator
Paste your raw, minified, or unformatted JSON payload into the input editor.
Select your preferred indentation size (2 spaces, 4 spaces, or tab indentation).
Click "Beautify" to format into human-readable nested structures.
If your payload contains syntax errors, the validator highlights the exact line number, column index, and invalid character.
Use "Minify" to strip all whitespace for production API payloads, or "Copy" to save to clipboard.
RFC 8259 JSON Data Types & Syntax Rules
JSON (JavaScript Object Notation) supports 6 core primitive and compound data types:
| Type | Format Example | Notes |
| :--- | :--- | :--- |
| **String** | `"username": "alex_dev"` | Must always be enclosed in double quotes `""` |
| **Number** | `"count": 42`, `"price": 19.99` | Integer or float; no hex or octal notations |
| **Boolean** | `"isActive": true` | Lowercase literal `true` or `false` |
| **Null** | `"deletedAt": null` | Lowercase literal `null` |
| **Object** | `{"id": 1, "role": "admin"}` | Key-value pairs enclosed in `{}` with unique string keys |
| **Array** | `["red", "green", "blue"]` | Ordered list of values enclosed in `[]` |
JSON Validation Best Practices for API Developers
- **Strict Double Quotes**: Keys must always use double quotes (`"key"` not `'key'`).
- **No Trailing Commas**: Unlike modern JavaScript object literals, JSON standards forbid trailing commas `[1, 2, 3,]`.
- **Unicode Encoding**: Escape non-ASCII or control characters with `\uXXXX` escape sequences to prevent parser breaks across heterogeneous microservices.
Frequently Asked Questions
Why is my JSON invalid? What are the most common syntax errors?
The three most common JSON errors are: (1) Using single quotes instead of double quotes for keys/strings, (2) Leaving a trailing comma after the last item in an array or object, and (3) Unescaped special characters (such as unescaped double quotes or unescaped backslashes).
Does this JSON Formatter upload my data to a server?
No. All parsing, validation, and beautification runs 100% client-side inside your browser sandbox. Your API responses, credentials, and sensitive configurations never leave your computer.
What is the maximum JSON file size this tool can format?
Because execution occurs locally using your browser memory and V8 JavaScript engine, it can comfortably format payloads of 20MB+ without network upload latency or timeout errors.
How do I convert formatted JSON back to a compact single-line string?
Simply click the "Minify" button. It removes all non-essential whitespace, line breaks, and indentation tabs, producing the most compact valid RFC 8259 JSON payload.