I built a free JSON toolkit with 68+ tools (security scanner, 19 language converters, offline PWA)

Json Web Tools — Mon, 02 Mar 2026 18:07:14 +0000

After a month of building, I launched jsonwebtools.com — a completely free JSON platform that works offline and never sends your data to a server.

Here’s what’s inside and why I built each feature.

The problem

Every time I needed to quickly decode a JWT, convert JSON to TypeScript, or compare two API responses, I found myself switching between five different sites. Half of them sent my data to their servers. Some required accounts. None worked offline.

So I built one tool that does everything.

What it includes

Core tools

JSON Validator — real-time validation with exact error line/column
JSON Formatter — 6 formatting styles (2-space, 4-space, tabs, aligned, sorted, compact)
JSON Repair — auto-fixes common errors (missing commas, single quotes, trailing commas)
JWT Decoder — decodes header, payload, signature with expiry check
JSON Diff — compares two JSON objects and highlights added/removed/changed fields

Security Scanner (my favorite feature)

Automatically scans JSON for:

XSS patterns (<script>, event handlers)
SQL injection attempts
Hardcoded credentials and API keys
PII data (emails, phone numbers, SSNs)
Path traversal patterns

Runs automatically on every validation — 100% client-side.

19 Language Converters

Paste JSON and get instant code in:

TypeScript, JavaScript, Python, Go, Rust, C#, Java, Swift, Kotlin, PHP, Ruby, GraphQL, Protobuf, OpenAPI/Swagger, Prisma, SQL, CSV, YAML, XML

Advanced tools

Batch Validator — drag & drop multiple JSON files
Performance Benchmark — measures parse/stringify/clone ops/sec
JSON to HTML Table — generates styled tables from JSON arrays
Size Analyzer — shows size breakdown by key and data type
JSON Masking — redacts sensitive fields (4 strategies)
Mock Data Generator — creates realistic test data
JSONPath Builder — visual query builder
JSON Patch (RFC 6902) and JSON Pointer (RFC 6901)

Technical implementation

Everything runs client-side using:

Monaco Editor (same editor as VS Code) for syntax highlighting
Service Worker for offline support (PWA)
localStorage for auto-save and snippets
Zero backend, zero database, zero cost to run

The security scanner uses regex patterns for known attack signatures. Not perfect, but it catches the obvious issues before they reach your API.

Command Palette (Cmd+K)

With 68+ tools, navigation became a problem. So I added a command palette — press Cmd+K and type any tool name. Fuzzy search works across all tools.

What I learned building this

Client-side is underrated. No server costs, complete privacy, works offline. For dev tools, this should often be the default.

Monaco Editor is incredible but heavy. It’s ~2MB loaded from CDN. Worth it for the VS Code experience, but something to watch for mobile users.

The security scanner is genuinely useful. While building it, I ran it on my own test JSON and discovered hardcoded API keys I had forgotten about.

Try it

👉 jsonwebtools.com — 68+ tools, free forever

I’d love feedback from developers — especially on the language converters (do the generated types/structs look correct?) and the security scanner patterns.

JSON Web Tools - 18 free JSON utilities in one place

Json Web Tools — Fri, 27 Feb 2026 07:14:31 +0000

Hey Dev community!

Just launched JSON Web Tools - a comprehensive suite of JSON utilities I built after getting tired
of juggling multiple bookmarks.

## What it includes

18 tools covering all JSON operations:

Validator (with actually helpful error messages)
JWT Decoder
Formatters & Minifiers
Converters (CSV, XML, YAML, SQL, Excel, TypeScript)
Schema Validator
Diff Checker
Tree View & Path Finder
And more!

## Why I built it

I was constantly switching between:

JSONLint for validation
JWT.io for decoding tokens
Various sites for conversions
Different tools for formatting

My bookmarks were a mess!

## Key features

✅ Privacy first - Everything runs client-side, your data never leaves your browser
✅ No signup - Just visit and use
✅ Completely free - No premium tier, no paywalls
✅ Fast - Vanilla JavaScript, no framework bloat
✅ Dark/light theme - Work comfortably anytime

## Tech stack

Pure JavaScript (no React/Vue/Angular)
Firebase Hosting
No backend needed
All processing client-side

## Try it

🔗 Live site: https://jsonwebtools.com
🚀 Product Hunt: https://www.producthunt.com/products/json-web-tools

Would love your feedback! What JSON tools do you use most?

DEV Community: Json Web Tools