JSON1

Free, private JSON tools that run entirely in your browser — www.json.how

JSON1 is 18 tools for reading, checking, and converting JSON: a formatter/validator, eight format converters, and nine type generators. Everything runs in JavaScript on your machine. There is no server to upload to, no account, and no data store — you can paste a production payload, then switch to airplane mode and keep working.

What's inside

• Formatter & validator — beautify, minify, and validate JSON with error positions, in a collapsible tree view.
• Format converters (8) — JSON ⇄ YAML, JSON ⇄ XML, JSON ⇄ TOML, JSON ⇄ CSV. The YAML converter quotes every scalar a YAML 1.1 loader would otherwise mistype (the Norway problem, sexagesimals, bare dates), checked against a real loader rather than its own reader.
• Type generators (9) — JSON → TypeScript, Java, Go, Python, C#, Rust, Kotlin, Dart, Swift. Every generator reads all records in an array, not just the first, so a field present in only some of them comes out optional instead of silently wrong.
• Knowledge base — 10 in-depth guides (syntax, escaping, JSON Schema, REST API design, parsing performance, type generation) in English, 简体中文, Español, and Português. Each language is written, not machine-translated.
• Privacy pages — Privacy, Terms, and Contact.

Tech stack

• Next.js 15 (App Router) + React 19 + TypeScript, exported as static files.
• Tailwind CSS 4 for styling, @heroicons/react for icons.
• Zustand for language/theme state, persisted to localStorage.
• i18next / react-i18next for the four-language interface.
• pnpm as the package manager.

Development

pnpm install
pnpm dev        # dev server (Turbopack) at http://localhost:3000
pnpm build      # static export to out/
pnpm lint       # ESLint

Tests

pnpm test       # generator + format converter correctness
pnpm test:wiki  # wiki content checks
pnpm test:pages # rendered-page verification (Python)
pnpm test:seo   # SEO/metadata verification (Python)

The generator and converter claims shown under each tool are checked against real output rather than proofread — that practice has caught real bugs.

Deployment

Deployed on Cloudflare Workers (static assets from out/). Pushing to main triggers a production build to www.json.how (the apex json.how redirects to www). The legacy json1.org domain 308-redirects here until it expires; its redirect lives on the old Vercel project.

Privacy

Nothing you paste into a tool leaves the browser. The site loads four third-party scripts — Google AdSense, Google Analytics, Microsoft Clarity, and Adsterra banners on wiki pages only — none of which receives editor contents; the full breakdown is on the About and Privacy pages. An ad blocker removes all four and every tool still works.