JSON Formatter & Validator — Beautify JSON Online
Format, validate, and beautify JSON in real time. Syntax highlighting, error line numbers, copy and download supported.
Paste JSON on the left to format it.About JSON Formatter & Validator — Beautify JSON Online
JSON Formatter & Validator is a free real-time tool that pretty-prints JSON instantly as you type, with syntax highlighting for keys, strings, numbers, and booleans. Syntax errors are shown with a detailed message. Configure indent width (2/4 spaces or tab), sort keys, copy, or download as a .json file. No registration required.
How to Use
- 1Paste your JSON into the left input area — the formatted result appears on the right instantly.
- 2Set indent width (2 spaces, 4 spaces, or tab) and toggle key sorting in the toolbar.
- 3If there is a syntax error, a red error message appears with the error details.
- 4Click "Copy" to copy the formatted JSON, or "DL" to download it as a .json file.
Features
- Real-time formatting with syntax highlighting as you type
- Color-coded output: keys (blue), strings (green), numbers (orange), booleans/null (purple)
- Syntax errors shown instantly with detailed error message
- Copy to clipboard or download as .json file
- Free and browser-based — data never leaves your device
JSON Syntax and Structure
JSON (JavaScript Object Notation) is a lightweight data-interchange format defined by RFC 8259. Understanding its syntax rules helps you write valid JSON and debug errors quickly.
Core Data Types and Rules
JSON supports six value types: objects (key-value pairs inside {}), arrays (ordered lists inside []), strings (double-quoted UTF-8 text), numbers (integers or decimals, no leading zeros), booleans (literal true or false), and null. All object keys must be double-quoted strings — single quotes are not allowed. Numbers cannot have leading zeros (01 is invalid) and cannot be NaN or Infinity. Trailing commas after the last element in an object or array are forbidden in standard JSON and will cause a parse error.
Common JSON Mistakes to Avoid
The most frequent JSON errors are: trailing commas ({"a":1,} is invalid), unquoted or single-quoted keys ({a:1} or {'a':1} are both invalid), using undefined or NaN as values (neither exists in JSON), and forgetting to escape special characters in strings (backslash, double-quote, and control characters must be escaped with a backslash). Comments are also not part of the JSON spec — remove any // or /* */ comments before parsing. Use this formatter to catch all these mistakes instantly.
JSON in Development Workflows
JSON is the de facto data format for web APIs and configuration files. Knowing how to work with it efficiently in your daily development workflow saves significant time.
Debugging API Responses
When an API returns a minified JSON response, it is nearly impossible to read at a glance. Paste the raw response body into this formatter to instantly see the structure with indentation and syntax highlighting. This is especially useful when debugging REST API calls in Postman, curl, or browser DevTools — just copy the response body from the Network tab and format it here to understand nested objects, find missing fields, or confirm that arrays have the expected number of elements.
Formatting Config Files and Pre-commit Checks
Configuration files like package.json, tsconfig.json, .eslintrc.json, and appsettings.json should be consistently formatted before committing to version control. Paste your config file here to normalize indentation (2 or 4 spaces are both common — pick one and stick to it). Enabling "Sort keys" alphabetizes object keys in config files, which makes git diffs cleaner and code reviews easier by ensuring keys always appear in a predictable order.
FAQ
- Does it validate JSON syntax?
- Yes. The tool validates as you type. Syntax errors are immediately shown in a red status message with the error detail.
- Can I use this to inspect API responses?
- Yes. Paste the raw JSON response from any API and it will be formatted and highlighted instantly.
- Will Unicode or emoji characters be escaped?
- No. Unicode characters including Japanese and emoji are rendered as readable text, not as \uXXXX escape sequences.
- Can I also minify JSON?
- For compression, use the JSON Minifier tool listed in the related tools section.
- Is there a key-sorting option?
- Yes. Enable "Sort keys" in the toolbar to sort all object keys alphabetically, making comparison easier.
- Does it support JSON5?
- No. This tool supports standard RFC 8259 JSON only. JSON5 features like comments or trailing commas are not supported.
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