Worktrees: isolated copies of your repo

Parallel work has a hidden hazard: two jobs editing the same project at once will trip over each other’s files. The fix is to give each one its own copy.

A worktree is a second, real checkout of your project on its own branch — so one branch can be live in one folder while another is live in a folder right next to it.

Normally your project folder shows one branch at a time. Switch branches and the files in that single folder change to match. Which means you can only be “on” one branch at once — and if Claude is working on branch B there, you can’t also do your own thing on branch A in the same folder.

A worktree breaks that limit. It’s a second folder, checked out to a different branch, sharing the same underlying repository. Branch A in your original folder, branch B in the worktree — both live, at the same time.

Not a copy-paste

This is the part that trips people up. A worktree is not “duplicate the files into a new folder.” That would drift out of sync and lose its connection to the project’s history.

It’s a genuine second checkout of the same repository. Same history, same set of branches available — just a different one checked out in each folder. Commit in the worktree and it lands in the same repo your original folder can see.

One repository, two (or more) working folders, each on its own branch.

What it’s for

This is the payoff of the whole level. Let an agent grind on a big change in a worktree while you keep working — or keep a second agent working — in the main folder. Different folders, different branches, no stepping on each other’s files.

It’s the physical version of the independence rule from the last two lessons: parallel work has to not collide, and separate folders guarantee it. (Tooling can spin worktrees up and clean them up for you, so you rarely manage them by hand.)

What’s next

That’s the end of Level 10 — and the edge of “you, in one sitting.” Everything here still had you in the chair: typing, watching, driving. Level 11 takes down the two walls that are left — connecting Claude to your other tools, and letting it run when you’re not there at all.