An offline JSON formatter that never sends your data
The JSON you need to read is usually an API response, and API responses usually contain a bearer token, a customer email, or an internal ID. Pasting that into a site that posts it to a backend is a habit worth breaking.
Start here
Every one of these runs entirely in your browser.
JSON Formatter
Format, validate, and beautify JSON data with syntax highlighting
In browserJSON Minifier
Minify JSON by removing whitespace and comments to reduce file size
In browserJSON Schema Validator
Validate JSON data against JSON Schema with detailed error reporting
In browserJSON Flattener/Unflattener
Flatten nested JSON objects or unflatten dot-notation objects
In browserAbout this page
The problem with pasting API responses into a web tool
Plenty of popular JSON formatters process server-side. The paste goes into a POST body, gets formatted somewhere else, and comes back. For public sample data that is fine. For a production response captured while debugging, you have just moved a live credential and real customer records onto infrastructure you do not control, usually in breach of whatever data policy your employer has.
It is also completely unnecessary. JSON parsing and serialisation are built into every browser. Formatting JSON needs no more infrastructure than a text box.
Genuinely offline, not just private
Once the page has loaded, the formatter keeps working with the network disconnected. That is the practical test for whether a tool is really client-side, and it is worth doing once on any tool you plan to trust: load it, go offline, and see if it still works.
It also means the tool is usable on a locked-down network, on a plane, or inside an environment where the sites that would normally do this are blocked by policy.
What it does beyond formatting
Validation reports the line and column of the first syntax error rather than just refusing, which is the part that actually saves time on a large document. There is a live byte, line, key and depth count, optional alphabetical key sorting, and minification for when you need the compact form back.
Keyboard shortcuts cover format, minify, copy and download, and large documents suspend format-as-you-type so the tab stays responsive instead of dropping keystrokes.
Frequently asked questions
Will it work with the network turned off?
Yes, once the page has loaded. All the code that formats and validates is already in your browser at that point. Reloading the page while offline needs the browser cache to still hold it, but the tool itself needs nothing further.
Is it safe to paste a production API response in?
The data does not leave your tab, so it is materially safer than a server-side formatter. Your own organisation's policy still applies, and you should check it. Nothing is stored in the page either, so closing the tab discards it.
How large a document can it handle?
Multi-megabyte documents format fine. Above roughly half a megabyte, formatting as you type is suspended automatically and you press the Format button instead, because re-serialising on every keystroke is what makes these tools feel broken on large files.