About JSON Validator & Formatter
A fast, free JSON formatter, validator and editor that treats your data the way it should be treated: it never sees it.
Private by design
Most online JSON tools send your document to a server to format or validate it. JSON Validator & Formatter doesn't have a server to send anything to. The entire application is static files, and every feature (parsing, validation, formatting, diffing, conversion) runs as JavaScript in your browser. Close the tab and it's gone; nothing was ever uploaded, logged or stored anywhere but your own device. That makes it safe for API payloads, configuration files and anything else you'd rather not paste into a stranger's server.
What it does
- Validate against RFC 8259, RFC 7159, RFC 4627 or ECMA-404, with line-precise, human-readable error messages and in-text highlighting.
- Auto-fix common mistakes in one click: trailing commas, single quotes, unquoted keys, comments, missing brackets.
- Edit visually in a tree or table view: click any key or value to change it, toggle booleans, pick colors, add or delete entries. Or edit raw text with syntax highlighting.
- Compare two documents side-by-side with a line diff.
- Convert & export to formatted JSON, minified JSON, YAML, CSV or plain text.
- Preserve big numbers with a lossless parser, so 64-bit IDs survive editing without silent precision loss.
- Share a document as a link, work in dark or light mode, and undo anything.
Free, forever
No account, no paywall, no usage limits, no ads. The tool is a static site with effectively zero running cost, so there is nothing to monetize you for.
How it's built
JSON Validator & Formatter is a single-page application built with React and Vite. The JSON tokenizer, linter, lossless parser, formatter and diff engine are all custom, dependency-free implementations, so the production bundle stays small and loads fast. Your documents and settings persist locally via your browser's storage, never remotely.
Feedback
Spotted a bug, or is there a feature that would save you time? Feedback is always welcome. The changelog shows how much of this tool exists because someone asked for it.