A no-upload JSON formatter that runs entirely in your browser

Every developer hits the same 30-second problem a dozen times a day: an API returns a wall of minified JSON, and you need to read it. You paste it somewhere, prettify it, maybe sort the keys, and move on.

The catch with "somewhere": a lot of online JSON formatters POST your payload to a server. When that payload is a production response with tokens, PII, or internal IDs, that's a quiet data-handling problem nobody signed off on.

The small rule I follow now

If a tool only transforms text, it has no business sending that text anywhere. Formatting JSON is pure string work — indent, parse, re-serialize. It can all happen on the client.

So when I need a quick format I use a client-side one: Toolonium's JSON formatter. The parsing and pretty-printing run in your browser; nothing is uploaded. No account, no paste-into-a-logged-server.

What it actually does

• Indent control: 2 spaces, 4 spaces, tab, or minify (min) to go the other way and compact a blob.
• Sort keys: alphabetize object keys — handy when you're diffing two responses that return fields in different orders.
• Quick stats: it reports the size in bytes, the key count, and the nesting depth. Depth is the sleeper feature: a surprise depth of 7 usually means your "flat config" grew a structure you didn't intend.

A tiny example of the kind of input it's built for:

{"project":"Toolonium","tools":["calculate","convert","create"],"free":true}

Formatted at 2-space indent that becomes readable in one click, and it'll tell you it's ~92 bytes with 3 top-level keys.

When to reach for it vs your editor

Your editor's formatter is great inside a file. A browser tool wins for the throwaway case: a response pasted from curl, a log line, a webhook body you're debugging in a meeting. No file, no project, no extension — just read it and close the tab.

And because it's client-side, it's safe to paste the ugly real-world payload, not a sanitized toy one.

Takeaway

Prefer formatters that transform locally. For JSON specifically, there's no reason the text should leave your machine. If you want a zero-upload one, try it here — it's free and there's nothing to install.

What's your rule for pasting production JSON into online tools? Curious how others handle the "is this thing uploading my payload" question.