The Changing Craft of Programming with John Crepezzi

Podcast: Signals and Threads (LS 43 · TOP 1.5% what is this?)
Episode: The Changing Craft of Programming with John Crepezzi
Pub date: 2026-10-16

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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:

QBasicPirates of Silicon ValleyHoogle — the Haskell API search engine that inspired the original code-search projectGitHub merge queue and CodespacesSorbet — gradual typing for Ruby; Hack — Meta’s typed PHPActive RecordBubblewrap and passt/pasta — sandboxing toolsseccomp BPFClaude Code and OpenAI Codex CLIModel Context Protocol and Agent SkillsPerfetto and magic-traceAntithesisBonsai — Jane Street’s OCaml web UI librarySignals & Threads: Language Design with Leo White

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