Episode 1: Six Concepts Explained

⏱ Est. reading time: 5 min Updated on 5/7/2026

What are Tool, Skill, Hook, Command, MCP, and Plugin? Why are some just Skills, while others include MCP services?

Quick Overview

Concept Explanation in One Sentence Analogy Example
Tool Built-in atomic operation capabilities of Claude Hands Read, Write, Edit, Bash
Skill Reusable workflows defined with Markdown Recipe /gsd-quick, /caveman, /mem-search
Hook Event-triggered automated scripts Automatic Door SessionStart to start services, PostToolUse to log
Command Slash commands exposed to users by a Skill Menu Item /setup, /configure
MCP External tool servers communicating via protocol Outsourced Team MySQL query, memory search, image analysis
Plugin Bundled distribution of Skill + Hook + MCP + Command Combo Meal claude-mem, caveman, claude-hud

Relationship Diagram

graph TB
    subgraph Claude Code Core
        TOOLS[Tools
Built-in atomic capabilities
Read/Write/Edit/Bash/...]
    end

    subgraph Extension Layer
        SKILLS[Skills
Defined in SKILL.md
Reusable workflows]
        HOOKS[Hooks
Event-triggered scripts
SessionStart/PostToolUse/...]
        MCP[MCP Servers
External tool services
stdio/SSE protocol]
    end

    subgraph Distribution Layer
        PLUGIN[Plugin
Bundled distribution unit
= Skills + Hooks + MCP + Commands]
    end

    subgraph User Interface
        CMD[Slash Commands
User input /xxx
Triggers Skill or Command]
    end

    PLUGIN -->|Contains| SKILLS
    PLUGIN -->|Contains| HOOKS
    PLUGIN -->|Contains| MCP
    PLUGIN -->|Contains| CMD

    SKILLS -->|Registered as| CMD
    CMD -->|Triggers| SKILLS
    SKILLS -->|Calls| TOOLS
    MCP -->|Exposes new| TOOLS2[MCP Tools
search/get_observations/...]
    TOOLS2 -->|Callable by Claude| TOOLS
    HOOKS -->|Event-triggered| AUTO[Auto Execution]

    style TOOLS fill:#2ecc71,color:#fff
    style PLUGIN fill:#9b59b6,color:#fff
    style MCP fill:#e74c3c,color:#fff
    style HOOKS fill:#f39c12,color:#fff
    style SKILLS fill:#3498db,color:#fff

Why are some just Skills while others include MCP?

It depends on the complexity of the functionality:

Type Requirements Example
Pure Skill Just Markdown instructions + Built-in Tools /gsd-quick: read, write, run commands—all built-in
Skill + Hook Needs auto-execution on specific events /caveman: SessionStart automatically activates compression mode
Skill + Hook + MCP Needs external data or services claude-mem: Needs search service, database, persistence
Skill + Command Needs multiple slash command entries claude-hud: /setup + /configure commands

Decision Criteria:

  • Use only Claude's native capabilities → Pure Skill
  • Need auto-triggering (startup, after each operation) → Add Hook
  • Need external data/services/databases → Add MCP Server
  • Need to distribute to other users → Pack into a Plugin