Skillintermediate

⚡ Layer 4: Execution Layer

Claude Code Knowledge Pack7/10/2026

Overview

🏠 Home › 🔧 Implementation › 🏛️ Architecture › ⚡ Layer 4: Execution

← 🔀 Delegation Layer ━━━━━━━━━━━━━━━━━━━━━●━━━━━━━━━━━━━━ 💾 State Layer →

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⚡ Layer 4: Execution Layer

Where actual work happens - code execution, file operations, API calls.

Purpose

The Execution Layer performs the actual work. It contains all the tools and subagents that carry out tasks delegated by the 🐔 Main Agent.

Components

Component	Emoji	Function	Spawned By
Subagents	🐦	Autonomous task execution	Task tool (🪺 spawn)
Built-in Tools	🔧	Core operations (Read, Write, Bash...)	🐔 Main Agent / 🐦 Subagents
MCP Tools	🔌	External services (Context7, Perplexity...)	🐔 Main Agent / 🐦 Subagents
User Interaction	💁‍♀️	Human-in-the-loop (❓ AskUser, 📋 Todo)	🐔 Main Agent / 🐦 Subagents

🐦 Subagent Lifecycle

%%{init: {'theme': 'base', 'themeVariables': {'lineColor': '#64748b'}}}%%
stateDiagram-v2
    [*] --> Spawned: 🪺 Task tool called
    Spawned --> Executing: Receives prompt
    Executing --> Working: Uses 🔧 🔌 💁‍♀️ tools
    Working --> Working: Iterates
    Working --> Completed: ✅ Task done
    Completed --> [*]: Returns result

    note right of Working
        🐦 Cannot spawn
        other subagents
    end note

Tool Categories

mindmap
    root(("⚡ Execution"))
        🔧 Built-in Tools
            🔧👀 Read file
                Read
            🔧🔍 Search content
                Grep
            🔧🗂️ Search files
                Glob
            🔧✏️ Write ops
                Write
                Edit
            🔧📟 Shell ops
                Bash
            🔧🌐 Web ops
                WebFetch
                WebSearch
        🔌 External MCP
            Context7
            Perplexity
            Firecrawl
            Custom MCPs
        💁‍♀️ User Interaction
            ❓ AskUserQuestion
            📋 TodoWrite
        🪺 Task spawn
            Spawns 🐦 Subagents

🔧 Built-in Tools Reference

Tool	Emoji	Operation
`Read`	🔧👀	Read file contents
`Write`	🔧✏️	Create/overwrite files
`Edit`	🔧✏️	Modify existing files
`Glob`	🔧🗂️	Search files by pattern
`Grep`	🔧🔍	Search content in files
`Bash`	🔧📟	Execute shell commands
`WebFetch`	🔧🌐	Fetch URL content
`WebSearch`	🔧🌐	Search the web

🔌 MCP Tools (External)

Tool	Purpose
Context7	Up-to-date library documentation
Perplexity	AI-powered web search
Firecrawl	Web scraping and crawling
Custom MCPs	Project-specific integrations

💁‍♀️ User Interaction Tools

Tool	Emoji	Purpose
`AskUserQuestion`	❓	Request clarification
`TodoWrite`	📋	Track task progress

🚂 Parallel Execution

%%{init: {'theme': 'base', 'themeVariables': {'lineColor': '#64748b'}}}%%
flowchart TB
    classDef main fill:#8b5cf6,stroke:#7c3aed,stroke-width:2px,color:#ffffff
    classDef subagent fill:#ec4899,stroke:#db2777,stroke-width:2px,color:#ffffff
    classDef state fill:#10b981,stroke:#059669,stroke-width:2px,color:#ffffff

    MA["🐔 Main Agent"]:::main

    MA -->|🪺 Task| SA1["🐦 Subagent 1"]:::subagent
    MA -->|🪺 Task| SA2["🐦 Subagent 2"]:::subagent
    MA -->|🪺 Task| SA3["🐦 Subagent 3"]:::subagent

    SA1 --> R1[Result 1]
    SA2 --> R2[Result 2]
    SA3 --> R3[Result 3]

    R1 --> MERGE["✅ Merge Results"]:::state
    R2 --> MERGE
    R3 --> MERGE

    MERGE --> MA

Parallel Execution Rules

Independence: Tasks must not depend on each other
No Cross-Communication: 🐦 Subagents cannot communicate directly
Single Orchestrator: Only 🐔 Main Agent coordinates
Result Aggregation: All results flow back to 🐔 Main Agent

Critical Rule

🐦 Subagents CANNOT spawn other 🐦 Subagents.

All delegation must flow through the 🐔 Main Agent.

❌ Wrong Pattern

🐔 Main Agent → 🐦 Subagent 1 → 🐦 Subagent 2  ❌ INVALID

✅ Correct Pattern

🐔 Main Agent → 🐦 Subagent 1
              → 🐦 Subagent 2
              → 🐦 Subagent 3

Layer Position

┌─────────────────────────────────────────────────────┐
│  🔀 LAYER 3: DELEGATION LAYER                       │
│  🦴 Slash Commands, 📚 Skills - workflow definition │
└─────────────────────────┬───────────────────────────┘
                          │
                          ▼
┌─────────────────────────────────────────────────────┐
│  ⚡ LAYER 4: EXECUTION LAYER  ◄─── YOU ARE HERE    │
│  🐦 Subagents, 🔧 Built-in, 🔌 External, 💁‍♀️ User   │
└─────────────────────────┬───────────────────────────┘
                          │
                          ▼
┌─────────────────────────────────────────────────────┐
│  💾 LAYER 5: STATE LAYER                            │
│  Memory, Files, Context - persistence               │
└─────────────────────────────────────────────────────┘

← 🔀 Delegation Layer ━━━━━━━━━━━━━━━━━━━━━●━━━━━━━━━━━━━━ 💾 State Layer →

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