JSON Formatter & Validator
Paste any JSON and instantly format it with proper indentation, validate its syntax, minify it to save space, or explore its structure in a collapsible tree view. Everything runs in your browser. Nothing is uploaded. Perfect for developers debugging API responses, config files and data payloads.
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When to use it
Read a one-line API response
Paste the single-line response you copied from the network panel and press "Format (Pretty)". Pick 2 spaces, 4 spaces or a tab for indentation, and use "Tree View" to open only the part you need.
Check a config file after editing
After changing package.json or another settings file, press "Validate" to confirm the syntax, the type at the top and how many items it has. If it is wrong you see where the problem is.
Shrink test data for a request body
Press "Minify" to remove every space and line break, then "Copy" the one-line result. The tool reports the new length in characters.
How to use
- Paste your JSON into the text area. You can paste raw API responses, config files or any valid JSON.
- Click "Format (Pretty)" to add indentation and line breaks. Choose between 2 spaces, 4 spaces or tabs. Click "Minify" to remove all whitespace for compact output. Click "Validate" to check if the JSON is valid.
- Use "Tree View" to explore nested objects and arrays as a collapsible tree. Click "Copy" to copy the result to your clipboard.
How it works
This tool uses JavaScript's built-in JSON.parse() to validate and parse JSON, and JSON.stringify() with indentation options to format it. The tree view recursively renders each node as collapsible HTML details/summary elements. All processing happens client-side in your browser, so your data never leaves your device. There are no external libraries, no server calls and no tracking. How to verify. Also available as a free REST API for developers and AI agents (edge-processed, zero retention).
FAQ
What does this JSON formatter do?
It pretty-prints JSON with your choice of indentation (2 spaces, 4 spaces or tabs), validates JSON syntax and highlights errors, minifies JSON by removing whitespace, and displays a collapsible tree view for exploring nested data.
Can it fix broken JSON?
It cannot auto-fix JSON, but it shows exactly where the error is (character position and surrounding text), so you can fix it yourself. Common issues include trailing commas, missing quotes and unescaped characters.
Is my data uploaded?
No. All processing runs locally in your browser using JavaScript's built-in JSON.parse and JSON.stringify. Nothing is sent to a server.
Is there a size limit?
There is no hard limit, but very large JSON (over 10 MB) may be slow to format or display in the tree view due to browser memory constraints.
Can I use this for API debugging?
Absolutely. Paste API responses here to quickly format and inspect them. The tree view is especially useful for exploring deeply nested API data.
Does it accept comments or single quotes?
Only standard JSON. Comments, single-quoted strings and a trailing comma after the last item are reported as invalid, so remove them and try again.
Why did a very long number change?
The tool uses JavaScript's JSON.parse, so integers above 9007199254740991 can lose their last digits. For IDs that must stay exact, check whether the original value is a string in quotes.
Can it sort keys, convert to XML or YAML, or open a file?
No. It formats, minifies, validates and shows a tree for JSON you paste in.
Last checked: October 9, 2026 · Dagochim team