Ruby on Rails web applications.

About

I'm Thimo Jansen. I build Ruby on Rails applications that make businesses work better — not just at launch, but for the years after.

What matters isn't the code. It's what you can do with it. A woodworker cares about the joints because you'll use the table every day; I care about tests and architecture for the same reason. The craft is in service of the thing, not the other way around.

I'm opinionated about how to build software, because I've been doing this since the 1990s and running Defrog on my own since 2009. Most of my work is with clients I stay with for years. Formed opinions save you from bad choices — that's what they're for.

Hire me and you get the whole tech side of the business. What I build, I own — not just through launch. No account managers, no handoffs, no “I'll have to check with the team.” You work with the person who writes the code. Hire me and we'll fix it.

Selected work

SportCity — Rails back-end, since 2020

I build, maintain, and host the Ruby on Rails back-end that powers SportCity's mobile apps and website. High-traffic, deeply complex — memberships, contracts, payments, and the systems that keep a fitness chain running. Flexible by design, because the business keeps evolving. Six years and counting.

TD SYNNEX — deal-processing tool, since 2000

Originally built the full e-commerce platform for ETC Distribution (later Tech Data, now TD SYNNEX) — one of the Netherlands' biggest ICT distributors. The scope is narrower today: a focused integration that imports vendor deals throughout the day and emails hundreds of tailored offers to customers.

Other work

Rails contracts over the years include Boom Uitgevers (publishing), HalloBoer (local-food marketplace) and JewelLabs (ticketing for theaters and cinemas). I've taught Ruby and Rails at Codaisseur Academy in Amsterdam, and created and contributed to many open-source projects along the way. I also build small dev tools on the side — macOS apps, MCPs, utilities. On GitHub.

What I do

Application development

Ruby on Rails web applications, front-end and back-end. Most of my work is highly technical back-end development — APIs, background jobs, payment processing, third-party integrations, data pipelines, admin interfaces. The parts most users never see but the business depends on.

New products from scratch, rewrites of systems that have outgrown what they were built for, and the tricky pieces others prefer not to touch.

Maintenance and upgrades

Taking on existing Rails applications that need ongoing care. Framework upgrades, paying down deferred maintenance, adding features the original build didn't anticipate. The work that keeps software making your business run better.

Managed hosting

For the applications I build, I also run them. PostgreSQL, background jobs, backups, monitoring, deploys via Kamal. Service levels tailored to what the system actually needs.

Stack

Ruby on Rails · Hotwire · Stimulus · PostgreSQL · Sidekiq · Kamal

What I reach for most. I'm open to whatever a project actually needs.