130+ Free Developer Tools That Run Entirely in Your Browser

The Security Problem With Developer Tools

Developers use online tools constantly — JSON formatters, Base64 encoders, JWT decoders. The problem is that developer data is often highly sensitive:

• JWT tokens contain user identity claims and session credentials
• API keys and secrets pasted into formatters can be logged by the service
• Database exports in JSON/CSV format contain production data
• Private keys pasted into converters
• Internal API payloads with PII, financial data, or business logic

When you paste a JWT token into a cloud-based JWT debugger, that token — which represents authentication credentials — is transmitted to their server. At best, it's logged for debugging. At worst, it's retained indefinitely.

For developer tools especially, the correct choice is local processing.

The Complete FusioFiles Developer Toolkit

JSON Tools

• JSON Formatter & Validator — format, minify, validate JSON. Supports jq-style queries.
• JSON to CSV Converter — flatten nested JSON to spreadsheet format
• JSON to YAML Converter — convert between serialisation formats
• JSON Path Tester — test JSONPath expressions against your data
• JSON Diff Tool — compare two JSON documents

Authentication & Security

• JWT Debugger — decode and inspect JWT header, payload, and signature. Zero server involvement — the token never leaves your browser.
• Hash Generator — MD5, SHA-1, SHA-256, SHA-512, SHA-3 hashes
• AES Encryption Tool — encrypt/decrypt text with AES-256 in CBC or GCM mode
• Password Generator — cryptographically random, fully configurable
• Password Strength Checker — entropy calculation, no data sent anywhere

Encoding & Decoding

• Base64 Encoder/Decoder — text and file Base64 conversion
• URL Encoder/Decoder — percent-encode/decode URLs and query strings
• HTML Entity Encoder — encode/decode HTML entities
• Base32 Converter — Base32 encoding for TOTP/MFA seeds
• Unicode Converter — code points, escapes, and character inspection

Generators

• UUID Generator — UUID v1, v4, and v7 generation
• Lorem Ipsum Generator — placeholder text in multiple formats
• Fake Data Generator — test names, emails, addresses, phone numbers
• Cron Expression Generator — build and explain cron schedules visually

Code Formatters

• SQL Formatter — format SQL queries with configurable dialect (MySQL, PostgreSQL, SQLite)
• HTML Formatter — prettify and minify HTML
• CSS Formatter — format and minify stylesheets
• JavaScript Formatter — prettify JS with configurable indent
• XML Formatter — format and validate XML

Testing & Debugging

• Regex Tester — test regular expressions with real-time match highlighting
• Markdown Editor — live preview markdown editor

Conversion Utilities

• YAML to JSON — convert YAML config files to JSON
• CSV to JSON — convert spreadsheet exports to JSON arrays
• Curl to Code — convert curl commands to Python, JS, Go, Ruby
• IP Subnet Calculator — CIDR notation, host ranges, broadcast addresses

Why These Are Better Than Alternatives

Most online developer tools (jwt.io being the famous exception for JWT) transmit your input to their servers. For production credentials, API keys, or internal data, this is a real security concern.

FusioFiles developer tools run zero server-side code. The processing happens in the browser's JavaScript engine and WebAssembly runtime. You can confirm this by opening Developer Tools → Network tab — no requests are made when you format, encode, or decode data.

Try the JWT Debugger — your token stays in your browser →