`git worktree` lets you check out multiple branches simultaneously in separate directories

If you are working on a feature branch and need to quickly check or test the main branch without stashing everything, `git worktree add` creates a second working directory linked to the same repository, checked out at any branch or commit. Changes in one worktree do not affect the other. Each worktree gets its own `HEAD` and index. When you are done, `git worktree remove` cleans it up.

# I create a worktree for main alongside the current feature branch
git worktree add ../main-check main

# I can now build and test main without touching my feature branch
cd ../main-check && npm run build

# I list all active worktrees
git worktree list

# I clean up when done
git worktree remove ../main-check