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Episode 1: Six Concepts Explained

5 MIN READ | UPDATED: 2026-05-07

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