I'll get to the depth stat in a second. First, the part nobody signs off on.

The upload you didn't agree to

A lot of web-based formatters POST your JSON to a server to "process" it. For a toy object, who cares. But the JSON you actually need to format is rarely a toy — it's a production API response with access tokens, customer emails, internal IDs, the stuff you'd never paste into a random third party on purpose. Formatting is pure string work: parse, indent, re-serialize. There is no technical reason for that text to leave your machine.

So my rule is simple: if a tool only transforms text, it transforms it in my browser or I don't use it. For JSON I reach for Toolonium's JSON formatter — everything runs client-side, nothing is uploaded, no account.

The stats that turn formatting into inspection

Beyond pretty-printing, the formatter reports three numbers, and the third is the one I actually watch:

• Size in bytes — a fast sanity check. "Why is this response 2 MB?" is a good question to ask before it hits a mobile client.
• Key count — how many keys at the top level. Handy for spotting a payload that quietly grew.
• Nesting depth — how many levels deep the structure goes. This is the sleeper. You think you have a flat config; the tool says depth 7. That depth is a map of accidental complexity — a settings.features.flags.experimental.rollout.v2.enabled that nobody meant to create.

A flat, intentional object sits at depth 2–3. When the number climbs past that without a reason, it's usually a sign the shape drifted over time and no one refactored it.

A couple of things it does well

• Indent control: 2 spaces, 4 spaces, tab — or minify to go the other way and compact a blob back down.
• Sort keys: alphabetize object keys. This one's underrated for diffing: two API responses that return the same fields in different orders look like a huge diff until you sort both and see they're identical.

When a browser tool beats your editor

Your editor's formatter is perfect inside a file. But half the time I'm formatting something that isn't a file yet: a response pasted straight from curl, a webhook body I'm reading in a meeting, a log line someone dropped in chat. No project, no extension, no file to save — just read it and close the tab. And because it's client-side, I don't think twice about pasting the real payload instead of a sanitized one.

Takeaway

Formatting JSON isn't just about indentation — glance at the depth and you'll catch structures that grew past what you intended. And prefer a formatter that transforms locally: there's no good reason a production response should be uploaded to read it. If you want a zero-upload one, it's here — free, nothing to install.

What's the deepest "flat config" you've ever found by accident? I'm collecting horror stories.