My name is Mariusz. I'm the CEO of Visuality, a boutique Ruby on Rails software house from Poland. I've been building software since 2007. I joined Visuality in 2014 as a Rails developer and worked my way up through team lead, engineering manager, CTO, and CEO since 2023, but my heart stays close to the code and, even more, to the people who write it. I'm probably best known for building the European Ruby community: I founded Ruby Europe, the Ruby Community Conference, and the Warsaw Ruby Meetup (PLRUG). I believe a strong language needs a strong community, and I spend a lot of my time making that happen.
This is what I'm most proud of. I bring Ruby people together across cities, countries, and companies.
- Ruby Europe - founded in 2024, an initiative to connect and strengthen the Ruby ecosystem across the continent.
- Ruby Community Conference - a conference built by enthusiasts for enthusiasts. It began in Warsaw in 2023 as the Ruby Warsaw Community Conference and grew into a recurring, international gathering (from 100+ developers at the first edition to 250+ attendees from 12 countries) that now lives in Kraków at the Manggha Museum of Japanese Art and Technology, a fitting home since Ruby was born in Japan. Five editions so far:
- Summer 2023 (Warsaw, July 2023, the very first edition): Nick Sutterer, Krzysztof Hasiński, Paweł Strzałkowski, and Sergey Sergyenko
- Winter 2024 (Warsaw, February 2024): Xavier Noria, Steven Baker, Michał Łęcicki, and Maciej Mensfeld
- Summer 2024 (Warsaw, July 2024): Hana Harencarova, Yaroslav Shmarov, John Gallagher, and Cristian Planas
- Winter 2025 (Kraków, February–March 2025): Aaron Patterson, Rosa Gutiérrez Escudero, Samuel Giddins, and Thomas Countz
- Winter 2026 (Kraków, March 13–14, 2026): Obie Fernandez, Marco Roth, Carmine Paolino, and José Valim
- PLRUG (Warsaw Ruby Meetups) - founded in 2022, a meetup for Ruby enthusiasts, hosted at Visuality's HQ.
Want to talk Ruby, community, or a possible collaboration? Grab a slot in my calendar.
Visuality is a specialized Ruby on Rails agency with 18 years of experience and deep seniority: engineers with an average of 9+ years on a single stack. We help companies rescue and scale digital products after the startup phase, modernize legacy, and bring AI to existing Rails applications. We don't try to be everything; we do one thing for a very long time, and we do it well.
I'm one of the experts behind Century Perspective, a consulting brand by Visuality that helps mature Rails products prepare for the AI era. Five experts with 100+ years of combined experience, who know Rails from the inside: no generic consulting, no rewrites from scratch. My focus is AI Business Strategy: turning AI opportunities into revenue and building a roadmap your board actually understands. Having walked the path from CTO to CEO, I look at AI through ROI, not technology for its own sake.
Almost all of my talks circle the same theme: building and growing the Ruby community. Some travelled to more than one event, so they're grouped by talk.
Building the Future of Ruby Through Community
Beyond Meetups: Creating a Ruby Ecosystem
- Rails World 2024 (lightning talk)
- Madrid.rb, November 2024
- Barcelona.rb, November 2024
Ruby Europe
- EuRuKo 2025 (lightning talk)
- Berlin Ruby + AI Meetup, June 2025
Why It's Important to Attend and Organize Ruby Meetups (lightning talk)
- RubyConf 2024
Panel: Baltic Region Communities - "Renaissance or Die"
- Baltic Ruby 2024
City Pitch: Warsaw
- EuRuKo 2023
More on my RubyEvents profile.
I write about people, knowledge, and running a company, and once in a while I still get my hands dirty with Rails internals:
- Ruby Community Conference: How It Started & What We Learned (LinkedIn)
- Things You Want to Know About 2022 in Visuality, but You're Too Afraid to Ask (2023)
- Successful Way to Transfer Technical Knowledge in an Organization (2022)
- We Started Using Event Storming. Here's Why! (2022)
- What You Lost When You Used structure.sql Instead of schema.rb in Your Rails Project (2022)
- Wizards and Kings: IndieRails, Episode 63, recorded at Rails World 2025 in Amsterdam, on building Visuality and the Ruby community
- Ruby community in Poland, how to become CTO and CEO: Friendly Show, Episode 9
- GitHub: @Adeptus · Visuality org: @visualitypl
- LinkedIn: koziel-mariusz
- X / Twitter: @KozieMariusz
- Visuality: visuality.pl