rederive

A skill for coding agents that teaches you a codebase by making you design it yourself. It only asks questions and never explains, until you work out why the code is built the way it is. Use it on a project your agent wrote for you, before an interview where you have to explain it, or on an open source repo like Express.

npx skills add EricJujianZou/rederive

Then type /rederive in your agent. Works in Claude Code, Codex, Cursor, Gemini CLI, GitHub Copilot, opencode, Windsurf, Amp, Goose and about 15 more. Needs git, bash and python3.

github.com/EricJujianZou/rederive → · MIT · 236★

A session

A rederive session on Express: it asks how you would send every HTTP request through one function, adds constraints, and you end up describing a middleware chain

How it works

It starts from why the project exists. On your own repo it asks why you built it. On someone else's repo it works out the original problem and asks how you would solve it.
A background agent maps the repo while you answer, from the code, the imports between files and the commits where the design changed. It doesn't trust commit messages, so repos built with AI in a few big commits work too.
The map holds 5 to 10 problems in the order the system would be built. When you're stuck it narrows each one to a few approaches to pick from.
It keeps notes on where you struggled and what you worked out alone, so you know what to practice.

Everything stays on your machine. rederive sends no telemetry.