About

About JSON Formatter Kit

JSON Formatter Kit is a free collection of 482 developer tools — formatters, validators, converters, encoders, generators and more — built on one principle: your data should never leave your device.

Why we built it

Most online formatters and converters send whatever you paste to their servers. That is a real problem when the “JSON” is an API response with customer records, a config file with credentials, or a JWT with personal claims. Developers paste sensitive data into these tools every day, often without thinking about where it goes.

JSON Formatter Kit started as a JSON formatter that works entirely in the browser, and grew into a full toolbox as we kept needing “just one more” utility that we didn’t want to trust to a random website.

How the privacy works — technically

• No server-side processing. The site is a set of static files served from a CDN. There is no application server that could receive your input. Formatting, parsing, hashing, encryption and conversion all run in JavaScript and WebAssembly inside your browser tab.
• Verifiable. Open your browser’s developer tools, switch to the Network tab and use any tool: you will see no request containing your data. The site also works offline once loaded — which would be impossible if it depended on a server.
• A strict Content Security Policy blocks third-party scripts, so no analytics or ad script can read what you type.
• The only network tools are the DNS lookups (which send only the domain you enter to Cloudflare’s public DNS resolver) and the API Tester (which sends only the request you build, to the URL you choose).

How we keep the tools accurate

• The JSON engine is a custom, lossless parser: large integers such as 64-bit IDs and number formats like 1.0 are preserved exactly, and every error comes with a line, column and plain-English explanation.
• Formatters use the same engines professionals rely on — Prettier, clang-format, Ruff, gofmt and others — compiled to run in the browser.
• Core logic is covered by automated tests, including official test vectors for hash functions (MD5, SHA-2, SHA-3, CRC, HMAC and more) and encodings.

Free, without accounts

Every tool is free and needs no sign-up. There are no usage limits, because your own device does the work.

Get in touch

Found a bug, want a tool we don’t have, or have feedback? Contact us — we read every message.