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 →Your Platform Has a Monolith, Too
GitHub published two incident reports in a single week. Both failures share the same structure: a system designed for a different scale, operating under conditions it wasn't built for.
Already Inside
The Vercel breach had nothing to do with AI-generated bugs. The attacker moved through doors that were already open. Containment has to extend beyond code boundaries.
Detection Won't Save You
AI-introduced vulnerabilities are now on the record. The teams reading these numbers as a detection problem are solving the wrong thing.
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.