I Built a Privacy-First Developer Toolbox That Runs 100% in Your Browser

Leo — Thu, 02 Apr 2026 12:52:28 +0000

Every developer has a handful of tools they reach for daily: a JSON formatter, a Base64 decoder, a timestamp converter. I got tired of pasting sensitive data into random websites that "promise" not to store it, so I built my own.

DevTools is a collection of 8 developer tools that run entirely client-side. No server uploads. No data collection. Everything happens in your browser tab.

What's Inside

JSON Formatter - Format, validate, and minify JSON with auto-detection of nested escaped strings
Base64 Converter - Encode and decode Base64 with full UTF-8 and emoji support
URL Encoder - Percent-encode/decode URLs with international character support
JWT Decoder - Decode JSON Web Tokens locally without ever sending your tokens to a server
Timestamp Converter - Convert between Unix timestamps and human-readable dates
UUID Generator - Generate cryptographically secure UUID v4 in bulk
Hash Generator - Calculate MD5, SHA-256, and SHA-512 hashes
Regex Tester - Test and debug regular expressions with live matching and replacement

Why Client-Side Matters

Think about what you paste into online tools every day:

JWT tokens containing user IDs and permissions
API responses with customer data
Configuration files with connection strings
Hashed passwords you're debugging

Most online tools send your input to a server for processing. Even if they don't log it intentionally, your data passes through their infrastructure. With client-side processing, the data literally cannot leave your machine.

You can verify this yourself: open the Network tab in your browser's DevTools while using any tool. You'll see zero outbound requests after the page loads.

Tech Stack

Next.js 16 with static export (output: "export")
React 19 for the UI
Tailwind CSS 4 for styling
CodeMirror for the code editors with syntax highlighting
Web Crypto API for hash generation (not a JS polyfill)
Deployed on Cloudflare Pages for global edge delivery

The static export means the entire site is pre-rendered HTML + JS. No server-side runtime, no API routes, no database. Just files served from Cloudflare's CDN.

A Few Things I'm Proud Of

Nested JSON detection: The JSON formatter auto-detects and recursively parses escaped JSON strings. If you have a log line where JSON is double-escaped ("{\"key\":\"value\"}"), it will unwrap it for you.

Hex UTF-8 decoding: Paste a string with \xE4\xB8\xAD and the formatter converts it to the actual Chinese character. Useful when debugging logs from Go or Python services.

Theme system: 7 built-in themes (Midnight, Dracula, Nord, Monokai, GitHub Dark, Solarized, Light) with instant switching and localStorage persistence. The theme loads before React hydrates, so there's no flash of wrong colors.

Cmd+K command palette: Quick-jump to any tool without touching the sidebar.

What's Next

I'm planning to add:

Color picker / converter (HEX, RGB, HSL)
Markdown previewer
Diff tool (compare two text blocks)
Cron expression parser

If you have suggestions for tools you'd find useful, I'd love to hear them in the comments.