Parallel Worktrees

Parallel Worktrees with Claude Code Subagents

Run multiple Claude Code agents simultaneously across git worktrees to transform a single developer into a team of AI engineers. LLM non-determinism becomes an advantage: running N parallel agents produces multiple valid solutions to choose from.

Table of Contents

• Core Workflow
• Git Worktrees Essentials
• Claude Code Subagents
• Spawning Parallel Subagents
• Workflow Patterns
• Dependency Management
• Common Pitfalls
• When to Use Parallel vs Sequential
• Resource Considerations
• Background Subagents with Worktree Coordination

Core Workflow

1. Create isolated worktrees for each task
2. Spawn independent Claude sessions in each
3. Cycle through to monitor progress and approve permissions
4. Merge the best results

Git Worktrees Essentials

Worktrees create additional working directories sharing a single .git database. Unlike cloning, they save disk space and keep history unified.

Key Commands

# Create worktree with new branch from main
git worktree add ../project-feature-a -b feature-a main

# Create worktree for existing branch
git worktree add ../project-bugfix bugfix-123

# Organized subdirectory pattern (recommended)
mkdir -p .worktrees && echo ".worktrees/" >> .gitignore
git worktree add .worktrees/feature-auth -b feature/auth main

# List all worktrees
git worktree list

# Remove worktree (use --force if uncommitted changes)
git worktree remove ../project-feature-a

# Clean stale metadata
git worktree prune

Directory Patterns

Adjacent folders: my-project/, my-project-feature-a/, my-project-bugfix/

Subdirectory pattern (keeps things organized):

my-project/
├── .worktrees/
│   ├── feature-auth/
│   ├── feature-api/
│   └── bugfix-login/
└── (main working tree)

Claude Code Subagents

Subagents are specialized AI assistants with isolated context windows, custom prompts, and configurable tool access.

Built-in Subagents

Creating Custom Subagents

Interactive: /agents command opens management menu (recommended)

File-based: Place markdown with YAML frontmatter in:

• .claude/agents/*.md (project-scoped)
• ~/.claude/agents/*.md (user-scoped)

---
name: code-reviewer
description: Expert code review specialist. Use PROACTIVELY after changes.
tools: Read, Grep, Glob, Bash
model: inherit
---

Acts as a senior code reviewer. When invoked:
1. Run git diff to see changes
2. Focus on modified files
3. Prioritize: Critical → Warnings → Suggestions

Note: Including "PROACTIVELY" or "MUST BE USED" in descriptions increases automatic invocation.

Spawning Parallel Agents

True parallelism requires separate Claude processes in different worktrees. Within a single REPL, subagents execute sequentially.

# Terminal 1
cd ../project-feature-a && claude

# Terminal 2
cd ../project-feature-b && claude

# Terminal 3
cd ../project-refactor && claude

Quick Setup Script

#!/bin/bash
# spawn-parallel.sh FEATURE_NAME NUM_AGENTS
FEATURE=$1
NUM=${2:-3}

for i in $(seq 1 $NUM); do
  git worktree add ".worktrees/${FEATURE}-${i}" -b "${FEATURE}-${i}" main
  cp .env ".worktrees/${FEATURE}-${i}/" 2>/dev/null || true
done

echo "Worktrees created. Start Claude in each:"
for i in $(seq 1 $NUM); do
  echo "  cd .worktrees/${FEATURE}-${i} && claude"
done

Custom Slash Commands

Create .claude/commands/init-parallel.md:

Create $NUM git worktrees for parallel development of $FEATURE.
1. Create .worktrees/ directory if needed
2. For each tree (1 to $NUM):
   - Create worktree at `.worktrees/$FEATURE-{i}/`
   - Create branch `$FEATURE-{i}`
   - Copy environment files
3. Print commands to start Claude in each

Workflow Patterns

Pattern 1: Parallel Feature Implementation

Create 3-4 worktrees for the same feature, give each identical instructions, compare results, merge best implementation.

Pattern 2: Explore, Plan, Code, Commit

1. Ask Claude to read relevant files (no writes)
2. Use thinking keywords ("think hard", "ultrathink") for extended reasoning
3. Have Claude create a plan document
4. Implement and commit

Pattern 3: Test-Driven Parallel

1. First Claude writes tests, confirms they fail, commits
2. Second Claude (or /clear) implements to pass tests
3. Third independent review catches overfitting

Pattern 4: Dual Claude Verification

1. One Claude writes code
2. After /clear or in different session, another Claude reviews
3. Fresh context catches issues original session missed

Essential CLI Reference

See references/cli-reference.md for the complete CLI command reference.

Key commands:

• claude - Start interactive session
• /clear - Reset context window
• /agents - Manage subagents

Dependency Management

Each worktree needs its own node_modules, venvs, etc.

# Fast copy (APFS/btrfs copy-on-write)
cp -c -r ../main/node_modules .  # macOS
cp --reflink=auto -r ../main/node_modules .  # Linux

# Deterministic install from lockfile
npm ci

# Copy environment files
cp ../main/.env . 2>/dev/null || true

Common Pitfalls

When to Use Parallel vs Sequential

Use parallel worktrees when:

• Multiple valid solutions exist (UI, algorithms)
• Complex tasks have failure risk (run 3, pick winner)
• Clear detailed plan exists for independent execution
• Features don't overlap in file modifications

Use sequential when:

• Critical refactors requiring consistency
• Tightly coupled changes to same files
• Merge conflicts would cost more than parallelism saves

Resource Considerations

• Token usage: ~15x higher with multi-agent workflows
• Subagents cannot spawn other subagents (no infinite nesting)
• Each subagent starts with clean context, needs codebase orientation
• Factor token consumption into subscription limits

Background Agents with Worktree Coordination

Claude Code natively supports background agents via the Task tool with run_in_background: true. This section codifies how background agents coordinate work across git worktrees for parallel task execution.

Architecture

Main Worktree (Orchestrator)
├── .agent-status/           # Coordination hub (tracked in .gitignore)
│   ├── task-api.json        # {"status": "RUNNING|COMPLETE|FAILED", "started": "...", "result": "..."}
│   └── task-ui.json
├── .agent-tasks/            # Task prompts for retry/reference
│   ├── task-api.md
│   └── task-ui.md
└── .worktrees/
    ├── task-api/            # Background agent 1
    │   └── RESULTS.md       # Agent writes summary here
    └── task-ui/             # Background agent 2
        └── RESULTS.md

Using Claude Code's Native Background Agents

Background agents are launched via the Task tool:

Task tool with:
  - run_in_background: true
  - prompt: "Work in .worktrees/task-api/. Implement the REST API..."
  - subagent_type: "general-purpose"

Use TaskOutput to check status and retrieve results when ready.

Worktree Setup for Background Agents

Before spawning background agents, prepare worktrees:

# Create worktrees for parallel tasks
./scripts/spawn-parallel.sh feature-api 1    # Creates .worktrees/feature-api-1/
./scripts/spawn-parallel.sh feature-ui 1     # Creates .worktrees/feature-ui-1/

# Or manually
git worktree add .worktrees/task-api -b task-api main
git worktree add .worktrees/task-ui -b task-ui main

Status File Convention

Background agents write status to .agent-status/TASK_NAME.json:

{
  "status": "COMPLETE",
  "started": "2024-01-15T10:30:00Z",
  "completed": "2024-01-15T10:45:00Z",
  "worktree": ".worktrees/task-api",
  "branch": "task-api",
  "summary": "Implemented 5 endpoints, 12 tests passing",
  "files_changed": ["src/api/users.ts", "tests/api.test.ts"]
}

Status values: RUNNING, COMPLETE, FAILED, BLOCKED

Agent Task Instructions Template

Include these instructions when spawning background agents:

## Task: [Task Name]
Work in the worktree at `.worktrees/[task-name]/`

### Requirements
[Specific task requirements]

### On Completion
1. Write a summary to `RESULTS.md` in the worktree
2. Commit all changes: `git add -A && git commit -m "[task-name]: [summary]"`
3. Update status file: Write to `../.agent-status/[task-name].json`:
   {"status": "COMPLETE", "summary": "[summary of accomplishments]"}

### On Failure
1. Document the issue in `RESULTS.md`
2. Update status: {"status": "FAILED", "error": "[what went wrong]"}

Orchestration Patterns

Pattern 1: Delegate and Continue

Orchestrator workflow:
1. Create worktrees for each task
2. Launch background agents with Task tool (run_in_background: true)
3. Continue working on primary task
4. Periodically check .agent-status/*.json files
5. When agents complete, review RESULTS.md and merge

Pattern 2: Fan-Out/Fan-In

1. Spawn N background agents for N independent subtasks
2. Each works in its own worktree
3. Use TaskOutput to wait for all to complete
4. Run ./scripts/sync-worktrees.sh to merge all results

Pattern 3: Pipeline with Dependencies

1. Background Agent A: Schema changes (no dependencies)
2. Wait for A to complete (check status file)
3. Background Agents B, C: API and UI (depend on schema)
4. Wait for B, C to complete
5. Merge in dependency order: A → B → C

Syncing and Merging Results

# Review all worktree changes
./scripts/sync-worktrees.sh --status

# Merge completed work to main
./scripts/sync-worktrees.sh --merge

# Interactive mode: review each before merging
./scripts/sync-worktrees.sh --interactive

Git-Based Signaling (Alternative)

For distributed setups or when status files aren't accessible:

# Background agent signals via branch push
git push origin task-api

# Main agent monitors
git fetch --all
git branch -r | grep -E "origin/(task-|feature-)"

# Check if branch has new commits
git log main..origin/task-api --oneline

Best Practices

1. One worktree per background agent: Ensures complete isolation
2. Non-overlapping file assignments: Prevents merge conflicts
3. Always write RESULTS.md: Provides context for merging
4. Commit before signaling complete: Ensures work is preserved
5. Use descriptive branch names: Makes merge history readable
6. Clean up after merge: Remove worktrees and status files
7. Set timeouts: Prevent runaway agents consuming resources

Checking Agent Status from Main Session

The main Claude session can monitor background agents:

# Quick status check
cat .agent-status/*.json | jq -r '.status'

# Detailed view
for f in .agent-status/*.json; do
  echo "=== $(basename $f .json) ==="
  cat "$f" | jq .
done

# Check if all complete
if grep -L '"status": "COMPLETE"' .agent-status/*.json; then
  echo "Some agents still running"
else
  echo "All agents complete - ready to merge"
fi