Rederive: learn a codebase by designing it yourself

Rederive asks how you'd solve the problem each part of the code exists for, then adds the project's real constraints until your answer matches what the authors built. It's a community skill by Eric Zou under the MIT license. The README says one install command covers Claude Code, Codex, Cursor, Gemini CLI, GitHub Copilot and about 15 other agents. For the basics, see Claude Code skills.

How a session runs

1. Type /rederive in a repo, or give it a local path or a git URL. A URL gets cloned into the current folder.
2. The first question is why the project exists. On your own repo it asks why you built it. On someone else's, it states the original problem in plain words and asks how you'd solve it.
3. While you answer, a background subagent maps the repo: the README, entry points, import links between files and the commits where the design changed. It trusts diffs over commit messages, so a repo built in a few big AI commits still works. The map holds 5 to 10 decisions in the order the system would be built, saved to .rederive/map.md. Don't open it before you finish. It has the answers.
4. Each decision starts as a problem with no constraints. Then they arrive one at a time: "with this, your design causes that; how would you change it?"
5. When you reach the real design, it names the technique as engineers know it, a middleware chain for example, and shows no code.

Stuck, it narrows the problem to a few options with their tradeoffs. Two wrong answers in a row and it offers a sketch of the problem, never of the missing piece. If your design beats the original, it says so.

Notes on where you struggled and what you worked out alone go to .rederive/log.md. The folder goes on the repo's local git exclude list, so none of it lands in a commit.

When to use it

• Before an interview about a project you built with AI help and can't yet defend line by line.
• Learning how a well-known open source project is put together.
• Joining a repo where you'll be changing the design itself.

To have the answers handed over instead, Understand Anything maps a codebase into a graph you can search and ask about. grill-me points the same kind of questioning at a plan you haven't built yet.

How to install it

npx skills add EricJujianZou/rederive

As a Claude Code plugin:

/plugin marketplace add EricJujianZou/rederive
/plugin install rederive@rederive

It needs git, bash and python3. Two bundled scripts read the git history and the import graph to build the map.

Example request

/rederive [local path or git URL]

I have about [30] minutes. Start with the root problem, stop after [two] problems, and tell me where my log is when we finish.

Limits

• It won't tell you a decision even if you ask. The SKILL.md has it add another constraint instead, though you can ask to skip a problem or start over.
• It treats the repo's code, comments and commit messages as material to teach from, never as instructions, and never runs the repo's code, scripts or tests. That's safer on an unknown repo, and it also means nothing gets checked by running it.
• The plugin is at version 0.1.0, first published in October 2026.