Stale Branch Detection

Identify git branches that are candidates for cleanup: merged-but-not-deleted and inactive branches with no recent commits.

Auto-Invoke Triggers

This skill automatically activates when:

1. Keywords: "stale branches", "old branches", "branch cleanup", "prune branches", "dead branches", "unused branches", "inactive branches", "branch hygiene"
2. Actions: "list branches to delete", "find stale branches", "clean up branches"

Arguments

• --threshold <months> — Inactivity threshold in months (default: 3)
• --base <branch> — Base branch for merge check (default: main)
• --remote — Include remote branch analysis

Workflow

Execute each step below using the Bash tool. This is a read-only skill — never delete branches, only report findings.

Step 1: Validate Git Repository

git rev-parse --is-inside-work-tree 2>/dev/null || echo "NOT_A_GIT_REPO"

If not a git repo, stop and inform the user.

Step 2: Parse Arguments

Parse $ARGUMENTS for:

• --threshold N → set THRESHOLD_MONTHS=N (default: 3)
• --base BRANCH → set BASE_BRANCH=BRANCH (default: main)
• --remote → set INCLUDE_REMOTE=true (default: false)

Verify the base branch exists:

git rev-parse --verify "$BASE_BRANCH" 2>/dev/null || echo "BASE_BRANCH_NOT_FOUND"

If the base branch doesn't exist, try master as fallback. If neither exists, stop and inform the user.

Step 3: Calculate Inactivity Threshold

Cross-platform threshold date (epoch seconds):

# macOS
if [[ "$OSTYPE" == "darwin"* ]]; then
  threshold=$(date -v-${THRESHOLD_MONTHS}m +%s)
else
  # Linux
  threshold=$(date -d "${THRESHOLD_MONTHS} months ago" +%s)
fi
echo "Threshold date (epoch): $threshold"

Step 4: List Merged Branches

Find local branches already merged into the base branch (safe to delete):

echo "=== MERGED BRANCHES (safe to delete) ==="
merged_count=$(git branch --merged "$BASE_BRANCH" | grep -v "^\*" | grep -vw "$BASE_BRANCH" | wc -l | tr -d ' ')
git branch --merged "$BASE_BRANCH" | grep -v "^\*" | grep -vw "$BASE_BRANCH" | while IFS= read -r branch; do
  branch="${branch## }"
  last_commit_date=$(git log -1 --format='%ci' "$branch" 2>/dev/null | cut -d' ' -f1)
  echo "  $branch  (last commit: ${last_commit_date:-unknown})"
done
if [ "$merged_count" -eq 0 ]; then
  echo "  (none)"
fi
echo "Total merged: $merged_count"

Step 5: Detect Squash-Merged Branches

Detect branches whose changes are already in base via squash-and-merge or rebase-merge. Uses git cherry to compare patch-ids — if all commits have equivalents in base, the branch is squash-merged and safe to delete.

echo "=== SQUASH-MERGED BRANCHES (safe to delete) ==="
squash_count=0
squash_list=""
for branch in $(git for-each-ref --format='%(refname:short)' refs/heads/); do
  [ "$branch" = "$BASE_BRANCH" ] && continue

  # Skip branches already detected as merged
  merged=$(git branch --merged "$BASE_BRANCH" | grep -w "$branch" | wc -l | tr -d ' ')
  [ "$merged" -gt 0 ] && continue

  # Count commits on branch since merge-base
  merge_base=$(git merge-base "$BASE_BRANCH" "$branch" 2>/dev/null)
  [ -z "$merge_base" ] && continue
  unique_commits=$(git log --oneline "$merge_base".."$branch" --no-merges 2>/dev/null | wc -l | tr -d ' ')
  [ "$unique_commits" -eq 0 ] && continue

  # git cherry: + means NOT in base, - means equivalent exists in base
  unpicked=$(git cherry "$BASE_BRANCH" "$branch" 2>/dev/null | grep '^+' | wc -l | tr -d ' ')
  if [ "$unpicked" -eq 0 ]; then
    relative=$(git log -1 --format='%cr' "$branch")
    echo "  $branch ($relative)"
    squash_count=$((squash_count + 1))
    squash_list="$squash_list|$branch"
  fi
done
if [ "$squash_count" -eq 0 ]; then
  echo "  (none)"
fi
echo "Total squash-merged: $squash_count"

Step 6: List Inactive Unmerged Branches

Find local branches NOT merged into base with no commits within the threshold period. Include ahead/behind counts:

echo "=== INACTIVE UNMERGED BRANCHES (review before delete) ==="
git for-each-ref --sort=committerdate --format='%(refname:short) %(committerdate:unix) %(committerdate:relative)' refs/heads/ | while IFS= read -r line; do
  branch=$(echo "$line" | awk '{print $1}')
  timestamp=$(echo "$line" | awk '{print $2}')
  relative=$(echo "$line" | cut -d' ' -f3-)

  # Skip base branch, current branch, and squash-merged branches
  [ "$branch" = "$BASE_BRANCH" ] && continue
  echo "$squash_list" | grep -qw "$branch" && continue

  # Check if branch is inactive (older than threshold)
  if [[ "$timestamp" =~ ^[0-9]+$ ]] && [ "$timestamp" -lt "$threshold" ]; then
    # Check if NOT merged
    merged=$(git branch --merged "$BASE_BRANCH" | grep -w "$branch" | wc -l | tr -d ' ')
    if [ "$merged" -eq 0 ]; then
      # Get ahead/behind counts relative to base
      counts=$(git rev-list --left-right --count "$BASE_BRANCH"..."$branch" 2>/dev/null)
      behind=$(echo "$counts" | awk '{print $1}')
      ahead=$(echo "$counts" | awk '{print $2}')
      echo "  $branch ($relative) [ahead $ahead, behind $behind]"
    fi
  fi
done

Step 7: Remote Branch Analysis (if --remote)

Only execute this step if --remote flag was provided.

Detect the remote for the base branch and fetch:

remote=$(git config --get "branch.$BASE_BRANCH.remote" 2>/dev/null || echo "origin")
if ! git fetch --prune 2>/dev/null; then
  echo "Warning: Could not reach remote. Skipping remote analysis."
fi

If the fetch warning was shown, skip the rest of Step 7. Otherwise, continue:

List remote merged branches:

echo "=== REMOTE MERGED BRANCHES ==="
remote_merged_count=$(git branch -r --merged "$BASE_BRANCH" | grep -v "HEAD" | grep -vw "$BASE_BRANCH" | wc -l | tr -d ' ')
git branch -r --merged "$BASE_BRANCH" | grep -v "HEAD" | grep -vw "$BASE_BRANCH" | while IFS= read -r branch; do
  branch="${branch## }"
  last_commit_date=$(git log -1 --format='%ci' "$branch" 2>/dev/null | cut -d' ' -f1)
  echo "  $branch  (last commit: ${last_commit_date:-unknown})"
done
if [ "$remote_merged_count" -eq 0 ]; then
  echo "  (none)"
fi

List remote inactive unmerged branches:

echo "=== REMOTE INACTIVE UNMERGED BRANCHES ==="
git for-each-ref --sort=committerdate --format='%(refname:short) %(committerdate:unix) %(committerdate:relative)' "refs/remotes/$remote/" | grep -v "HEAD" | grep -vw "$BASE_BRANCH" | while IFS= read -r line; do
  branch=$(echo "$line" | awk '{print $1}')
  timestamp=$(echo "$line" | awk '{print $2}')
  relative=$(echo "$line" | cut -d' ' -f3-)

  if [[ "$timestamp" =~ ^[0-9]+$ ]] && [ "$timestamp" -lt "$threshold" ]; then
    merged=$(git branch -r --merged "$BASE_BRANCH" | grep -w "$branch" | wc -l | tr -d ' ')
    if [ "$merged" -eq 0 ]; then
      echo "  $branch ($relative)"
    fi
  fi
done

Step 8: Summary

Present a summary report:

current_branch=$(git branch --show-current)
total_local=$(git branch | wc -l | tr -d ' ')
merged_into_base=$(git branch --merged "$BASE_BRANCH" | grep -vw "$BASE_BRANCH" | wc -l | tr -d ' ')

echo "=== SUMMARY ==="
echo "Current branch: $current_branch"
echo "Base branch: $BASE_BRANCH"
echo "Inactivity threshold: $THRESHOLD_MONTHS months"
echo "Total local branches: $total_local"
echo "Merged into $BASE_BRANCH: $merged_into_base"
echo "Squash-merged (detected via git cherry): $squash_count"

After the summary, suggest cleanup commands (but never execute them):

Cleanup commands (run manually):
  Delete merged local:   git branch -d <branch>
  Delete unmerged local:  git branch -D <branch>
  Delete remote:          git push origin --delete <branch>
  Delete all merged:      git branch --merged main | grep -v main | xargs git branch -d

Important Caveats

• Squash merges: Branches merged via squash-and-merge are detected using git cherry (patch-id comparison). Edge cases where detection may fail: amended commits after squash, or partial cherry-picks. If a branch appea