I kept reaching for online JSON tools and closing the tab because they either uploaded my data to a server, buried the editor under ads, or split "validate / format / convert" across five different sites.

JSON FYI does it all client-side: validate (with exact line/column + a fix hint), format, minify, tree-view, JSONPath test, diff, and convert to CSV/XML/YAML, plus a JSON Schema validator (Ajv). Nothing leaves your browser; it works offline once loaded.

There's also a /learn library of error-diagnostic guides — e.g. every "Unexpected token in JSON" / Python JSONDecodeError / Postgres invalid input syntax for type json message mapped to its cause and fix: https://www.jsonfyi.com/learn/common-json-errors

Built with TanStack Start (SSR) + React. Feedback on the validator's error messages especially welcome.