JSON Formatter & Validator — Free Online Tool
Paste JSON to format, validate, minify, or view as a tree — entirely in your browser.
How It Works
- 1Paste your JSON into the input area.
- 2Choose Format to pretty-print or Minify to strip whitespace.
- 3Copy the result with one click.
About JSON Formatter
Working with JSON data from an API response, configuration file, or database export? Unformatted JSON is nearly impossible to read, especially when deeply nested. This tool formats messy JSON into readable, properly indented output with syntax highlighting and line numbers, making it easy to scan and understand the structure of your data. It validates your JSON in real time and shows clear, descriptive error messages for invalid input — helping you quickly locate missing commas, unmatched brackets, or other syntax issues. Toggle between formatted and minified views with one click, which is useful when you need compact JSON for API requests or configuration files. You can also view your data as a collapsible tree, making it easy to explore deeply nested structures by expanding and collapsing nodes. Common use cases include debugging API responses, formatting configuration files for readability, validating JSON payloads before sending them, and minifying JSON to reduce payload size.
From the blog
Frequently Asked Questions
Is my JSON data sent to a server?
No. All formatting happens in your browser using JSON.parse and JSON.stringify. No data leaves your device.
What's the difference between Format and Minify?
Format adds indentation and line breaks for readability. Minify removes all whitespace to produce the smallest possible output — useful for APIs and configuration files.
Can it handle large JSON files?
It works well for JSON up to a few megabytes. Very large files may cause the browser tab to slow down due to rendering the formatted output.
Is my file uploaded to a server?
No. Transmute processes everything locally in your browser using JavaScript and the Canvas API. Your files never leave your device — there is no server, no upload, no cloud processing.
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