using-git-worktrees

Using Git Worktrees

Overview

A worktree is an exception for simultaneously checking out another Git history, not a general safety badge. Prefer the current workspace and reuse an existing suitable worktree. A branch decision and a worktree decision are separate.

Core principle: create only with necessity and ownership evidence; pair every created worktree with a cleanup path.

Announce at start: explain which concrete checkout conflict requires a worktree.

Step 0: Environment Detection

Before mutation, record the repository root, HEAD, branch/detached state, staged/unstaged/untracked paths, active Git operations, and:

git worktree list --porcelain

Stop on detached HEAD, unresolved conflicts, or an active merge/rebase/ cherry-pick/revert/bisect. Preserve user state: no automatic stash, reset, clean, broad staging, or commit.

Before deciding necessity or placement, read the smallest relevant project AGENTS.md, CLAUDE.md, current authority, and existing worktree convention. Repository policy may require or forbid isolation and owns any approved in-repo location; do not discover that policy after creating the checkout.

Step 1: Necessity Decision

Create at most one task-owned worktree only when one of these is true:

• another branch must remain checked out while this task proceeds;
• unrelated dirty state prevents a safe checkout in the current workspace;
• explicit user or current repository authority requires it.

Task complexity, planning, TDD, use of subagents, or a main/master branch name is not sufficient. Same-task subagents share one workspace; do not create per-subagent or nested worktrees. If independent history is unnecessary, do not create a branch either.

Record: reason, branch, exact path, creating coordinator, and expected cleanup event. If the owner or cleanup condition is unknown, stop before creation.

Step 2: Safe Placement

Use an existing repository convention only when the target directory is already ignored (git check-ignore). Never edit or commit .gitignore solely to host a worktree. If no safe in-repo convention exists, use a task-specific external user-level temporary directory outside the repository. Resolve and verify the exact path before creation; do not target a broad home, workspace, or repo root.

Step 3: Create the Minimum Checkout

Prefer reusing an existing branch carrying the same goal. Create a branch only when the approved Git lifecycle requires independent history.

# Existing branch
git worktree add <exact-path> <branch>

# New independently justified branch
git worktree add -b <branch> <exact-path> <start-point>

Read back git worktree list --porcelain, the new worktree's HEAD/branch, and its status. Do not use force flags.

Step 4: Authority-Led Setup and Baseline

Read the project's install docs, lockfiles, and existing setup scripts. Run only setup the project explicitly requires. Do not infer npm install, cargo build, pip install, poetry install, or dependency downloads merely from manifest presence.

Run the smallest relevant baseline verification. If setup or tests fail, report the exact failure and preserve the worktree; do not hide it by mutating unrelated files.

Step 5: Handoff and Cleanup Ownership

Report the exact path, branch, start HEAD, baseline result, owner, and cleanup trigger. The creating coordinator remains responsible until it proves cleanup or explicitly hands ownership off.

Use finishing-a-development-branch after the task commit or integration decision. A worktree may usually be removed while its unmerged branch remains; an open PR does not require a permanent checkout.

Red Flags

Never:

• create a worktree only because a task modifies code;
• modify .gitignore merely to make worktree creation possible;
• install dependencies blindly;
• create one worktree per subagent;
• run global prune or force cleanup as routine hygiene;
• remove dirty, untracked, locked, user-owned, or ownership-unknown resources.

Integration

Called conditionally by planning/execution workflows only after the necessity decision. Pairs with finishing-a-development-branch for evidence-led cleanup.