codebase-onboarding-maplisted

# Codebase Onboarding Map ## Install Save this file as `~/.claude/skills/codebase-onboarding-map/SKILL.md`, or `.claude/skills/codebase-onboarding-map/SKILL.md` to scope it to one repo. Claude Code auto-discovers it. Invoke with `/codebase-onboarding-map` or by asking "help me understand this codebase". ## Why this exists The expensive part of a new codebase is not reading it. It is not knowing which 10% matters, which parts are load-bearing, and which comment is a lie left over from a refactor two years ago. READMEs describe intent at the moment someone had time to write. Code describes what is true now. Where they disagree, the code wins, and the gap between them is one of the most useful things you can hand a newcomer. **This produces a map, not a summary.** A summary tells someone what exists. A map tells them where to go and what will hurt. ## Step 1 — Establish the shape before reading anything deeply ``` git log --oneline -20 git log --format='%an' | sort | uniq -c | sort -rn | head cat package.json 2>/dev/null || cat pyproject.toml go.mod Cargo.toml Gemfile 2>/dev/null rg --files | sed 's|/[^/]*$||' | sort | uniq -c | sort -rn | head -25 ``` You are answering: what kind of project, what stack, how many people, still moving or dormant, and which directories carry the weight. Directory file counts beat any architecture diagram, because they are generated from reality. ## Step 2 — Trace ONE request end to end This single step teaches more than any amount of fi