Ruby has a distinct culture around idiomatic code. The language is designed so that well-written Ruby reads almost like English — concise, expressive, and elegant. AI-generated Ruby often misses this: the code works, but it reads like Ruby written by someone who learned Python first.

A CLAUDE.md file at your repo root tells your AI assistant what "good Ruby" looks like for your project. Here are 13 rules that matter most.

Rule 1: Ruby version and runtime environment

Ruby version: 3.3+. Use YJIT in production ( `RUBY_YJIT_ENABLE=1` or `--yjit` ). Bundler manages all gems — no manual `require` for anything in the Gemfile. `.ruby-version` file is authoritative for local development.

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Ruby 3.x has significant performance improvements and new syntax. AI often generates code compatible with Ruby 2.x.…