I Built 14 Free Tools for Developers AND People Who Hate Spreadsheets

Magnus Silverstream — Sun, 22 Mar 2026 11:30:29 +0000

Every day I generate UUIDs, encode Base64 strings, and convert timestamps. On weekends, I compare mortgage scenarios and plan retirement savings. I got tired of juggling five different websites — none of them doing everything I needed — so I built the toolbox I actually wanted to use every day.

That's SD6 Tools.

What's in the box

14 tools, split across four categories:

Security & Generators

Password Generator — Cryptographically secure, 8-128 chars, strength indicator
UUID/GUID Generator — v4 UUIDs with bulk generation and multiple formats
QR Code Generator — URLs, text, WiFi configs, with customizable output

Finance Calculators

Mortgage Calculator — Compare up to 4 scenarios side-by-side, full amortization schedules, 5 payment frequencies
Retirement Calculator — Compound growth projections with inflation, employer matching, visual charts
Auto Loan Calculator — Tax, insurance, and trade-in breakdown
Compound Interest Calculator — See the power of compounding over time
Savings Goal Calculator — Target-based savings planning
Debt Payoff Calculator — Snowball vs avalanche strategy comparison
Gas vs Electric Calculator — Total cost of ownership comparison

Developer & Converter Tools

Text Encoder — Base64, URL, HTML entities, Unicode, hex
Base Converter — Binary, octal, decimal, hex
Unit Converter — Hundreds of units across length, weight, temperature, and more
Timestamp Converter — Unix timestamps ↔ human-readable dates

Why not just use Calculator.net or CyberChef?

Fair question. Here's what's different:

1. Privacy-respecting by default

No cookies until you explicitly opt in. No account creation. All calculations run client-side in your browser — your mortgage numbers never leave your machine. Analytics are consent-based and anonymized.

2. Four languages, not an afterthought

English, French, Spanish, and German — with locale-aware formatting. A German user sees 1.234,56 € while an American sees $1,234.56. This matters when your mortgage calculator shows six-figure numbers.

3. Tools I actually use every day

This isn't a weekend project I abandoned. I use these tools daily — UUID generation while coding, Base64 encoding for API debugging, unit conversions for international projects, and the mortgage calculator when reviewing my own loan options. Every feature exists because I needed it myself.

4. Real scenario comparison

The mortgage calculator lets you compare up to 4 loan scenarios side-by-side. Change the rate, the term, the payment frequency — see the impact instantly. Most free calculators give you one result. This gives you the full picture.

The tech stack

For those curious:

React 18 + TypeScript 5 — Standard modern stack
Vite 5 — Fast builds, HMR
Tailwind CSS — Utility-first styling
Recharts — Financial charts and visualizations
react-i18next — Internationalization with <50ms language switching
Pre-rendered static HTML — Every page is pre-rendered for SEO. No empty SPA shells.
Cloudflare Pages — Free hosting, global CDN

What I learned building this

Multilingual SEO is hard. Getting hreflang tags, canonical URLs, and pre-rendered content right for 4 languages × 14 tools × blog articles = 276 URLs was a significant challenge. Google doesn't make it easy.

Financial precision matters. JavaScript floating-point arithmetic will betray you. 0.1 + 0.2 !== 0.3 becomes a real problem when calculating 300 monthly mortgage payments. Every calculation is validated against known financial formulas.

Dark mode is expected. It was one of the first feature requests. Every tool supports it.

What's next

More tools are in active development — hash generators, JSON formatters, regex testers, and more. The codebase supports adding new tools quickly thanks to a shared component architecture.

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

Try it: sd6tools.net
Blog: sd6tools.net/blog

All tools are free. No signup required. Just tools.

DEV Community: Magnus Silverstream