Context Fork Skill

Context Fork Skill

This skill demonstrates the context: fork feature, which allows a skill to run in an isolated sub-agent context with its own conversation history and state.

What is Forked Context?

When a skill uses context: fork, it:

1. Creates a new sub-agent: A separate agent instance is created
2. Isolates conversation history: Has its own independent context
3. Provides clean state: No contamination from the main conversation
4. Can specify agent type: Uses the agent field to determine sub-agent behavior

When to Use Forked Context

✅ Good Use Cases

1. Complex Multi-Step Operations

   • Long-running analyses that shouldn't clutter main conversation
   • Multi-phase processing with intermediate states

2. Isolated Testing

   • Test code without affecting main context
   • Experiment with different approaches

3. Specialized Agent Behavior

   • Need specific agent type (Plan, Explore, etc.)
   • Different tool access patterns

4. State Management

   • Keep temporary state isolated
   • Prevent unintended side effects

❌ Avoid When

1. Simple one-shot tasks (overhead not worth it)
2. Need to share results immediately (forked context is isolated)
3. Real-time collaboration required (context is separate)

Configuration

Skill Metadata

context: fork           # Enables forked context
agent: general-purpose  # Specifies agent type

Available Agent Types

• general-purpose: Default agent for general tasks
• Plan: Planning and design focused
• Explore: Codebase exploration and analysis
• code-reviewer: Code review specialist
• custom: Custom agents defined in .claude/agents/

Testing Forked Context

Test 1: Basic Isolation

Ask me to perform a complex analysis:

Analyze this codebase and create a detailed report

Behavior:

1. A new sub-agent is created
2. The analysis runs in isolation
3. The main conversation stays clean
4. Results are returned when complete

Test 2: Conversation History

Test that the forked context has separate history:

First, tell me your name in the forked context
Then ask in the main conversation what we discussed

Expected: The main conversation won't see the forked context's internal messages

Test 3: Different Agent Types

Test with different agent types:

# For planning tasks
context: fork
agent: Plan

# For exploration
context: fork
agent: Explore

# For code review
context: fork
agent: code-reviewer

Advanced Features

1. Combining with Hooks

Forked context works with hooks:

context: fork
agent: general-purpose
hooks:
  PreToolUse:
    - matcher: "Bash"
      hooks:
        - type: command
          command: "echo 'Forked context: Running Bash'"

2. Tool Restrictions

Limit tools in forked context:

context: fork
agent: general-purpose
allowed_tools:
  - Read
  - Grep
  # No Write - read-only analysis

3. Model Selection

Use specific model in forked context:

context: fork
agent: general-purpose
model: claude-sonnet-4-20250514

Comparison: Forked vs Non-Forked

Implementation Details

Architecture

Main Conversation
    ↓
    User requests task using context-fork-skill
    ↓
Skill Engine
    ↓
    Detects context: fork
    ↓
Sub-Agent Factory
    ↓
    Creates new agent instance
    ↓
Forked Context
    ↓
    Executes task in isolation
    ↓
    Returns results
    ↓
Main Conversation (receives results)

Memory Considerations

Forked context:

• ✅ Has its own context window
• ✅ Doesn't compete with main context for tokens
• ⚠️ Uses additional memory (sub-agent instance)
• ⚠️ Results still consume tokens when returned

Performance

Forked context overhead:

• Creation: ~100-200ms
• Execution: Same as normal (no penalty)
• Cleanup: ~50ms

Total overhead: ~150-250ms per invocation

Best Practices

DO ✅

1. Use for complex tasks

   • Multi-step analyses
   • Long-running operations
   • Stateful processing

2. Choose appropriate agent

   • Plan for design tasks
   • Explore for code analysis
   • general-purpose for general tasks

3. Combine with tool restrictions

   • Read-only for analysis
   • Specific tools for specific tasks

4. Document the isolation

   • Explain why forked context is used
   • Clarify what's isolated

DON'T ❌

1. Don't use for simple tasks

   • One-shot queries don't need isolation
   • Adds unnecessary overhead

2. Don't forget about isolation

   • Results need to be explicitly returned
   • Can't access main conversation state

3. Don't overuse

   • Each fork consumes resources
   • Multiple concurrent forks can be expensive

4. Don't assume shared state

   • Forked context starts fresh
   • No memory of previous interactions

Testing Checklist

Verify forked context behavior:

• Sub-agent is created
• Conversation history is isolated
• Agent type is respected
• Tool restrictions work
• Results are returned correctly
• No contamination of main context
• Cleanup happens after completion
• Works with hooks
• Works with model selection

Troubleshooting

Fork Not Creating

Problem: Skill runs in main context

Solutions:

1. Verify context: fork is in YAML frontmatter
2. Check YAML syntax (no tabs, proper indentation)
3. Ensure agent field is specified

Wrong Agent Type

Problem: Uses default agent instead of specified one

Solutions:

1. Check agent name spelling
2. Verify agent exists (for custom agents)
3. Use built-in agent names (general-purpose, Plan, Explore)

Results Not Returned

Problem: Forked context completes but no results

Solutions:

1. Ensure skill returns output
2. Check for errors in forked context
3. Verify execution completed successfully

Examples

Example 1: Code Analysis

---
name: deep-code-analysis
description: Perform deep code analysis in isolation
context: fork
agent: Explore
allowed_tools:
  - Read
  - Grep
  - Glob
---

Usage:

Analyze the authentication system deeply

Example 2: Security Audit

---
name: security-audit
description: Run security audit in isolated context
context: fork
agent: general-purpose
allowed_tools:
  - Read
  - Grep
  - Bash
hooks:
  PreToolUse:
    - matcher: "Bash"
      hooks:
        - type: command
          command: "echo 'Security audit: Executing command'"
---

Example 3: Planning Task

---
name: architecture-planner
description: Create architecture plan in isolation
context: fork
agent: Plan
---

Usage:

Create a detailed plan for refactoring the payment system

Summary

Forked context provides:

• ✅ Isolated execution environment
• ✅ Separate conversation history
• ✅ Configurable agent types
• ✅ Clean state management
• ✅ No contamination of main context

Use when you need isolation, complex processing, or specialized agent behavior.

Version: 1.0.0 Last Updated: 2026-01-10 Maintainer: SDK Team