About tooljo

tooljo is a small collection of tools — for developers, finance, and fitness — that aim to be the fastest path between "I need to do X" and X being done. Each tool lives on its own subdomain, ships under 30 KB, and works in your browser.

The premise

Most online tools are 5 MB single-page apps that take three seconds to render an empty text input, plus an email gate, plus an upsell. tooljo is the opposite: each tool ships as static HTML under 30 KB, no signup, and renders instantly.

Everything runs in your browser. No accounts, no upload, no request to a server you have to trust. UUIDs you generate on guid.tooljo.com, JSON you format on json.tooljo.com, mortgage scenarios you compute on finance.tooljo.com — none of it touches our infrastructure. You can verify by opening DevTools → Network and pasting anything you want.

Each subdomain is independently deployable; a single shared Caddy on the VPS routes by Host header. Press ⌘K on any page for the cross-network command palette — it auto-detects what you've pasted (UUID, JWT, JSON, color, timestamp, hash) and jumps to the right tool.

Who runs it

Built and maintained by Samuel Yoo (@samuelyoo). Background in software engineering, building tools and infrastructure for production systems. tooljo started as a side project to learn where SEO economics actually work for static sites in 2026.

Editorial standards

Articles cover technical topics — UUID versions, database primary-key strategy, mortgage amortisation, training pace zones, cryptographic hash selection. Each one is written from direct experience and references the relevant RFCs, library source, benchmarks, or domain-standard texts (Daniels' Running Formula for pace zones, RFC 1321 for MD5, FIPS 180-4 for SHA-2, etc.). When something is uncertain or contextual, the article says so — there are no "definitive" answers to design questions masquerading as facts.

Articles include a last updated date. When a UUID library or spec changes (e.g. RFC 9562 in 2024, Python's uuid7() in 3.13, .NET 9's Guid.CreateVersion7()), the relevant pages get updated and the date refreshes.

Open source

The site is built with Astro, deployed to a Hostinger VPS with Caddy. The repository is currently private; the underlying generation logic uses the well-known uuid npm package and the browser's crypto.randomUUID().

Monetization, transparently

tooljo plans to display ads from networks like Google AdSense or Carbon Ads to cover hosting and development time. Ads will be clearly marked, will not interrupt the tools, and will not track you across sites without consent. There are no plans to add upsell modals or paywalls to existing tools.

A future paid API tier (for high-volume server-side operations on the developer tools — UUID, JSON, base64, regex, JWT, hash) is in design. Free, in-browser tools will remain free and ad-supported. Sign up below if you want to be notified when the API launches.

Contact

Bug reports, content corrections, or feature requests: email hello@tooljo.com. Replies usually within a few days.