JSON Lint & Formatter

“JSON formatter / validator” is one of the most-used developer searches, yet the popular tools are ad-cluttered, slow, and — worse — quietly upload your data to a server to validate it. And almost all of them point you at the wrong place when JSON is broken: modern browsers report the most common mistakes (a trailing comma, a missing value) with no position at all, so these tools just say “error on line 1”. There was room for a fast, private, genuinely accurate version.

I built the engine as a pure, unit-tested module: parse, format, minify, deep key-sort and structure stats, with zero dependencies. The hard part was error location — modern V8 reports common errors as “Unexpected token … snippet …” with no line number, so I wrote a recovery step that reconstructs the exact offset from the engine's snippet. The result is a single-screen editor with a line gutter, live validation as you type, and a clickable error banner that drops your cursor right on the problem. Everything runs client-side, so nothing you paste ever leaves your machine. I stress-tested it against classic JSON gotchas and round-tripped nearly 800 real-world JSON files from open-source projects with zero mismatches.