15 Free Developer Tools That Run Entirely in Your Browser

The best small developer tools have three things in common: they're fast, they don't require a login, and — crucially — they process your data in the browser so nothing sensitive is uploaded to a server. Here are 15 we reach for constantly, all free and all client-side.

Formatting & data

• JSON Formatter — beautify, minify, and validate JSON with exact error messages.
• JSON to TypeScript — generate types from a sample API response.
• JSON ↔ CSV — convert an array of objects to a spreadsheet and back.
• Text Diff Checker — compare two blocks line by line.

Encoding & security

• Base64 Encode / Decode — with full Unicode support.
• JWT Decoder— inspect a token's header and payload without sending it anywhere.
• Hash Generator — SHA-256/384/512 via the Web Crypto API.
• URL Encoder / Decoder — percent-encode query values safely.
• Password Generator — strong, secure random passwords.

Text & conversion

• Regex Tester — test patterns with live matches and capture groups.
• Case Converter — camelCase, snake_case, kebab-case, and more.
• Find & Replace — bulk replace with regex support.
• Number Base Converter — binary, octal, decimal, hex.

Handy utilities

• UUID Generator — cryptographically random v4 IDs.
• CIDR / Subnet Calculator — network, broadcast, host range, and mask from a prefix.

Why "in the browser" matters

Many online tools quietly upload whatever you paste to their servers. For a JWT, an API response, or an internal config, that's a real risk. Every tool above runs entirely on your device — the data never leaves your machine, so they're safe even for sensitive input. It's also faster: no round-trip to a server.

Browse the full set on the tools hub — there are more than 45, spanning developer, converter, text, calculator, and generator categories.