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About

Last updated: 12 September 2026

JSON Tool is a free, single-page utility that formats, minifies and validates JSON. It is an independent project maintained by one developer, and the whole tool is one HTML file with no backend of its own.

What it does

• Format — pretty-prints JSON with an indent width you choose from 1 to 20.
• Minify — strips all whitespace to shrink a payload.
• Validate — reports the exact parser error when the input is not valid JSON.
• Sort keys — recursively, including objects nested inside arrays, so two payloads can be compared line by line.
• Read it comfortably — line numbers, character counts, a light and dark theme, copy to clipboard, and download as formatted.json.

Who it is for

Developers eyeballing an API response, analysts inspecting a JSON export, anyone debugging a payload that came back malformed. It is also usable when you have no idea what JSON is: paste, press Format, read the result.

The design priority is that sensitive payloads stay on your machine. Config dumps, tokens, customer records and internal API responses are exactly the things that should not be pasted into a website that uploads them somewhere to reformat them. So this one does not.

How it works

Formatting happens in your browser using the JavaScript engine's own JSON parser — the same code path your browser uses to read JSON. Nothing is sent to a server for processing, and there is no queue, storage or log of what you paste. After the page has loaded you can disconnect from the network and keep working.

What it deliberately does not do

• No account, no sign-in, no usage limits, and no paywall.
• No server-side processing of your JSON, and no ability to recover anything you typed.

Known limits

It accepts strict JSON only. Comments, trailing commas, single quotes, JSON5, JSONC and newline-delimited JSON (NDJSON) are rejected — that is the JSON parser's behaviour, not a bug. There is no JSON Schema validation, no JSONPath query, no diff view and no conversion to or from YAML, XML or CSV.

Because everything runs in your tab, very large inputs are bounded by your browser's memory and can make the tab unresponsive. Split files over a few megabytes rather than pasting them whole.

Cost

Free, with no paid tier. What is and is not collected is described in full in the privacy policy.