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 Review Queue is Not the Problem
On teams with high AI adoption, PR review time increases 91%. The instinct is to treat that as the problem to solve. It isn't.
The Reliability Gap
Amazon has a gap between how fast AI can generate change and how fast its systems can safely absorb it. Most organizations haven't registered the shift yet.
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 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.