Introducing Catalyst: 100 Free Developer Tools That Never Phone Home

Catalyst is a single-page toolbox of 100+ developer utilities — JSON formatter, JWT decoder, regex tester, password generator, CSS gradient builder, and dozens more — and every one of them runs entirely in your browser. Your data is never sent to a server, never logged, and never cached. You can verify it by disconnecting your network and watching every tool continue to work.

This post is a short explanation of why Catalyst exists, what's inside it, and how it's built.

The problem with online dev tools

Most online developer tools look like utilities but behave like data collection endpoints. When you paste a JSON payload into a random formatter site, you have no way to know whether it was logged, indexed, cached, or sold. For hobby data this is uncomfortable; for production API responses, customer PII, or internal config files, it is a compliance incident waiting to happen.

The frustrating part is that none of this collection is necessary. Every common developer task — JSON parsing, Base64 encoding, SHA-256 hashing, AES encryption, regex matching, image resizing, SVG optimization — can run in pure JavaScript on the user's device. The browser already has everything needed. There is no technical reason to send anything to a server.

What's in the box

Catalyst bundles 100+ tools into 12 category toolkits:

• JSON & Data — format, minify, repair, diff, and convert between CSV, YAML, XML, TypeScript, and Markdown
• Text & String — word counter, case converter, diff, find/replace, slug generator, lorem ipsum
• Encode/Decode — Base64, URL, HTML entities, hex, ASCII, Unicode, ROT13, Base32, JWT decoder
• Hash & Security — MD5, SHA-1/256/512, HMAC, AES-256-GCM encryption, JWT builder, password generator
• Code Tools — JS/CSS/HTML/SQL/XML/YAML format and minify, plus Markdown live preview
• Web & HTTP — HTML preview, regex tester, URL parser, user agent decoder, meta tag generator
• CSS & Design — gradient, box shadow, border radius, flexbox, color picker, palette generator
• Converters — number base, color, data size, Roman numerals, Unix timestamp, date difference
• Generators — UUID, QR code, random values, credit card / IBAN / email validators, regex library
• Image Tools — to/from Base64, SVG optimizer, image resizer, color picker
• DevOps & Config — cron explainer, chmod, .env parser, MIME lookup, semver, .gitignore generator
• AI Tools — MCP config explorer, system prompt builder, agent skills reference for Claude development

Every tool has its own URL you can bookmark and link directly.

How it stays private

Three technical choices keep your data off our servers:

1. Static pre-rendered HTML

Catalyst is a Next.js application built with static generation (SSG). Every tool page is a pre-rendered HTML file served from a CDN. There is no application server that sees your requests with body payloads.

2. Native Web APIs for everything heavy

Cryptographic tools use the browser's native crypto.subtle API — the same implementation that powers TLS and WebAuthn. Random values come from crypto.getRandomValues(), a CSPRNG suitable for security-sensitive use. JSON, YAML, XML, and Markdown parsers run as bundled JavaScript libraries that execute locally.

3. Zero analytics on tool inputs

Catalyst uses basic page-view analytics (no cookies, no fingerprinting), but tool inputs and outputs are never captured anywhere in the code. You can audit this in the network tab: after the page loads, no requests fire regardless of what you paste.

What's next

The current toolset covers the 100 most common tasks I reach for as a developer, but there are more. Over the coming weeks we're adding more tools, richer content for each one, and direct deep links so you can share a specific tool with a teammate.

If there's a tool you use daily that would fit Catalyst's philosophy — free, client-side, no friction — let me know. The roadmap is driven by what developers actually need.