Every developer has hit the same wall: an API returns a response, you log it to check something, and instead of readable data you get one unbroken line of text a thousand characters long. JSON is designed to be compact for transmission, not for a human to read — which is exactly the gap a formatter exists to close.
What formatting actually does
A JSON formatter re-indents the same data with consistent spacing and line breaks, so nested objects and arrays are visually obvious instead of buried in a wall of braces. Nothing about the underlying data changes — keys, values, and structure are identical before and after. It's purely a readability transform, which is also why it's safe to format something before you've fully understood what's in it.
Reading the error message
The more useful half of a good JSON formatter is what happens when the input is actually broken: a missing comma, an unclosed bracket, a trailing comma before a closing brace. Rather than failing silently, a proper parser reports the exact character position where it got confused — which is almost always right at, or just after, the real mistake. Learning to read that position instead of scanning the whole blob by eye is the fastest way to fix malformed JSON.
Going from JSON to something else
JSON rarely lives in isolation. Config files are increasingly written in YAML for readability, spreadsheets export to CSV, and auth tokens are Base64-encoded JSON under the hood. Tools like YAML ⇄ JSON, CSV ⇄ JSON, and a JWT decoder cover the conversions that come up constantly around JSON specifically, without needing a script for a one-off check.
Minifying for production
The same tool works in reverse: once you're done editing or debugging, minifying strips the indentation and line breaks back out before the JSON goes into a config file or gets sent over the wire, shaving off bytes that serve no purpose once a human doesn't need to read it anymore.