Joe Leo
Founder & CEO, Def Method
I founded Def Method in 2014 with a simple premise: the most valuable engineering work happens when the stakes are high and getting it wrong isn't an option.
I've helped engineering teams at companies like Citi, Walmart, and Paxos modernize systems that couldn't afford to break. Revenue-critical platforms. Regulated environments. Operationally sensitive infrastructure.
I'm also the co-author of The Well-Grounded Rubyist (now in its 4th edition) and co-host of The Ruby AI Podcast, where we explore the intersection of Ruby and artificial intelligence.
Speaking & Podcast
I regularly speak at conferences about Ruby, Rails, and engineering leadership. I'm also the co-host of The Ruby AI Podcast.
Latest Insights
View all →The Bull Case for Ambition
Abundance does not eliminate opportunity. It expands it. But it also clarifies what was always true: the constraint was never intelligence. It was imagination.
The Platform Illusion: Why AI Won't Save Incremental Software
The market is pricing architectural courage. Companies that simply 'add AI' to existing products won't survive. The winners will rebuild around it.
The Price of Agency
Both OpenClaw and Gas Town imbue LLMs with an agency that stirs strong emotions. One side expresses wonder at what's now possible. The other expresses fear at potential downsides. Both deserve serious attention.
The Well-Grounded Rubyist
4th Edition — Co-authored with David A. Black
The Well-Grounded Rubyist is a comprehensive guide to Ruby that has helped thousands of developers master the language. Now in its 4th edition, it covers Ruby 3.x and modern Ruby idioms while maintaining the deep, thorough approach that made it a classic.
Whether you're new to Ruby or looking to deepen your understanding, this book provides the foundation you need to write confident, idiomatic Ruby code.
Want to work together?
If you're facing a Rails modernization challenge where getting it wrong isn't an option, let's talk.