Using Git Worktrees

Overview

Ensure work happens in an isolated workspace. Prefer your platform's native worktree tools. Fall back to manual git worktrees only when no native tool is available.

Core principle: Detect existing isolation first. Then use native tools. Then fall back to git. Never fight the harness.

Workspace policy: every change is written on its own branch. The default is a worktree; a simple feature branch in the main checkout is an exception the human requests explicitly. The base branch is never written to. This skill applies at three trigger points:

1. Session start — report the current branch, whether the working directory is a worktree and the active change. Do not create anything yet.
2. Before creating change artifacts — isolate first if the current branch is the base branch.
3. Before implementing a plan — same check.

Announce at start: "I'm using the using-git-worktrees skill to set up an isolated workspace."

Step 0: Detect Existing Isolation

Before creating anything, check if you are already in an isolated workspace.

GIT_DIR=$(cd "$(git rev-parse --git-dir)" 2>/dev/null && pwd -P)
GIT_COMMON=$(cd "$(git rev-parse --git-common-dir)" 2>/dev/null && pwd -P)
BRANCH=$(git branch --show-current)

Submodule guard: GIT_DIR != GIT_COMMON is also true inside git submodules. Before concluding "already in a worktree," verify you are not in a submodule:

# If this returns a path, you're in a submodule, not a worktree — treat as normal repo
git rev-parse --show-superproject-working-tree 2>/dev/null

If GIT_DIR != GIT_COMMON (and not a submodule): you are already in a linked worktree. Skip to Step 2. Do NOT create another worktree. Report: "Already in isolated workspace at <path> on branch <name>." (Detached HEAD: note that branch creation is needed at finish time.)

If GIT_DIR == GIT_COMMON (or in a submodule): you are in a normal repo checkout. Resolve consent from the preference already declared in AGENTS.md or the session instructions. When the declared default is a worktree, do not ask again. Ask only when no preference exists:

"Would you like me to set up an isolated worktree? It protects your current branch from changes."

If the user declines, work in place only when they asked for a simple feature branch and the working tree is clean. Never work on the base branch: isolate, or stop and ask. Record the exception in the change.

Step 1: Create Isolated Workspace

Two mechanisms. Try them in this order.

1a. Native Worktree Tools (preferred)

Do you already have a way to create a worktree? It might be a tool named like EnterWorktree, WorktreeCreate, a /worktree command, or a --worktree flag. If so, use it and skip to Step 2. Native tools handle directory placement, branch creation and cleanup automatically; using git worktree add when you have one creates phantom state your harness cannot see or manage.

1b. Git Worktree Fallback

Only if Step 1a does not apply.

Directory Selection

Explicit user preference always beats observed filesystem state.

1. Check your instructions for a declared worktree directory preference.
2. Check for an existing project-local directory: ls -d .worktrees (preferred) or ls -d worktrees. If both exist, .worktrees wins.
3. Otherwise default to .worktrees/ at the project root.

Safety Verification (project-local directories only)

MUST verify the directory is ignored before creating the worktree:

git check-ignore -q .worktrees 2>/dev/null || git check-ignore -q worktrees 2>/dev/null

If NOT ignored: add it to .gitignore, commit, then proceed. Prevents accidentally committing worktree contents.

Create the Worktree

path="$LOCATION/$BRANCH_NAME"
git worktree add "$path" -b "$BRANCH_NAME"
cd "$path"

Sandbox fallback: if git worktree add fails with a permission error, tell the user the sandbox blocked it and work in the current directory instead.

Step 2: Project Setup

Run the project's install command from AGENTS.md § Comandos (INSTALL_COMMAND). If it is N/A, skip this step. Do not guess stack-specific commands.

Step 3: Verify Clean Baseline

Run the project's test command (TEST_COMMAND). If it is N/A, state that there is no automated baseline.

If tests fail: report failures and ask whether to proceed or investigate. If they pass: report ready.

Report

Worktree ready at <full-path>
Tests passing (<N> tests, 0 failures)
Ready to implement <feature-name>

Quick Reference

Red Flags

Never:

• Write on the base branch: isolate the change or stop and ask
• Create a worktree when Step 0 detects existing isolation
• Use git worktree add when you have a native worktree tool (e.g., EnterWorktree)
• Skip Step 1a by jumping straight to Step 1b's git commands
• Create a worktree without verifying it's ignored (project-local)
• Skip baseline test verification
• Proceed with failing tests without asking

Always:

• Run Step 0 detection first
• Prefer native tools over git fallback
• Follow directory priority: explicit instructions > existing project-local directory > default
• Verify the directory is ignored for project-local
• Use the project's INSTALL_COMMAND / TEST_COMMAND
• Verify a clean test baseline

References

Read only when needed:

• references/common-mistakes.md — the five recurring mistakes and their fixes.