The Changing Craft of Programming with John Crepezzi

John Crepezzi has spent his career building tools for other programmers—at Tumblr, at Square, and then at GitHub, where he worked on the merge queue and the early versions of Codespaces. He came to Jane Street to build a code search engine for OCaml. A week into the job, ChatGPT came out, and he’s been working on AI tooling ever since. In this episode, Ron and John talk about how a three-day prototype grew into a firmwide platform for agentic coding, how AI can break the social contract around code review, and how to build tools that support both agent workflows and human understanding.
You can find the transcript for this episode on our website.
Some links to topics that came up in the discussion:
QBasic
Pirates of Silicon Valley
Hoogle — the Haskell API search engine that inspired the original code-search project
GitHub merge queue and Codespaces
Sorbet — gradual typing for Ruby; Hack — Meta’s typed PHP
Active Record
Bubblewrap and passt/pasta — sandboxing tools
seccomp BPF
Claude Code and OpenAI Codex CLI
Model Context Protocol and Agent Skills
Perfetto and magic-trace
Antithesis
Bonsai — Jane Street’s OCaml web UI library
Signals & Threads: Language Design with Leo White