Generate Onboarding Document

Crawl a repository and generate ONBOARDING.md at the repo root -- a document that helps new contributors understand the codebase without requiring the creator to explain it.

Onboarding is a general problem in software, but it is more acute in fast-moving codebases where code is written faster than documentation -- whether through AI-assisted development, rapid prototyping, or simply a team that ships faster than it documents. This skill reconstructs the mental model from the code itself.

This skill always regenerates the document from scratch. It does not read or diff a previous version. If ONBOARDING.md already exists, it is overwritten.

Core Principles

1. Write for humans first -- Clear prose that a new developer can read and understand. Agent utility is a side effect of good human writing, not a separate goal.
2. Show, don't just tell -- Use ASCII diagrams for architecture and flow, markdown tables for structured information, and backtick formatting for all file paths, commands, and code references.
3. Six sections, each earning its place -- Every section answers a question a new contributor will ask in their first hour. No speculative sections. Section 2 may be skipped for pure infrastructure with no consuming audience, producing five sections.
4. State what you can observe, not what you must infer -- Do not fabricate design rationale or assess fragility. If the code doesn't reveal why a decision was made, don't guess.
5. Never include secrets -- The onboarding document is committed to the repository. Never include API keys, tokens, passwords, connection strings with credentials, or any other secret values. Reference environment variable names (STRIPE_SECRET_KEY), never their values. If a .env file contains actual secrets, extract only the variable names.
6. Link, don't duplicate -- When existing documentation covers a topic well, link to it inline rather than re-explaining.

Execution Flow