Stop Switching Tabs — One Free Tool Replaces All Your JSON & Dev Tools

Every day I was doing the same thing:

• Paste API response into some random formatter


• Open another tab to decode the JWT


• Open another tab for Base64


• Open another tab to test a regex

Four tabs. Same tools. Every single day.

So I built JsonMaster — a free developer toolbox that puts 12 tools in one tab.

👉 https://jsonmaster.netlify.app/

No login. No ads. Your data never leaves your browser.

What's Inside

JSON Formatter & Validator

Paste raw minified JSON and instantly see it beautified. Built on Monaco Editor — the same engine as VS Code — so you get syntax highlighting, inline error squiggles, code folding, and keyboard shortcuts you already know.

JSON Converters

Convert JSON to:

• 
  YAML — for Kubernetes, Docker Compose, GitHub Actions


• 
  CSV — for Excel, Google Sheets, data pipelines


• 
  XML — for legacy systems and SOAP APIs


• 
  TypeScript Interface — paste an API response, get a typed interface instantly


• 
  Zod Schema — instant runtime validation schema for TypeScript projects


• 
  .env file — flatten nested JSON config into environment variables

JWT Decoder

Paste any JWT. See header, payload, signature decoded instantly. Checks expiry and algorithm. Everything happens in your browser — nothing is sent to a server.

Base64 & URL Encoder / Decoder

Encode or decode Base64 and URL strings instantly. Handles Unicode correctly. Useful for decoding auth headers, query strings, and embedded images.

Regex Tester

Write a pattern, test it against your input in real time. Every match is highlighted. Supports all JS regex flags: g, i, m, s, u. Shows match groups and count.

JSON Diff & Compare

Paste two JSON objects. See exactly what was added, removed, or changed — down to the specific key path. Useful for comparing API responses before and after a deploy.

Why Client-Side Matters

Most JSON tools send your data to a server. You paste a JWT or production API response — it travels over the network to someone's backend.

JsonMaster is 100% client-side. Open DevTools → Network tab while using it. You will see zero outgoing requests for your data.

This matters when you're working with JWT tokens, API responses with user data, or config files with credentials.

Try it free → https://jsonmaster.netlify.app/

Drop a comment if you find a bug or want a new tool added. I read everything.