Concepts

Claude Code lets you extend the assistant with six kinds of objects. They have similar-sounding names and they show up in different sections of CLACOROO, so it’s worth getting the vocabulary right.

This page is the glossary. The Features section is where you act on each of these objects.

The six objects

marketplace  →  plugin  →  ┬→  skill
                           ├→  agent
                           ├→  MCP server
                           └→  hook

Read top to bottom: a marketplace ships plugins; each plugin can bundle one or more skills, agents, MCP servers and hooks. CLACOROO has one sidebar section per box.

Marketplace

A marketplace is the source from which you install plugins. In practice, a marketplace is a Git repository (or a local folder) with a marketplace.json manifest that declares which plugins are available.

You add a marketplace once; it then exposes a catalog of plugins you can install. You can also remove a marketplace when you no longer want any of its plugins.

Examples:

• An official organization repo with vetted plugins
• Your own private marketplace with internal plugins
• A local folder with experimental plugins you’re testing

CLACOROO section: Marketplaces.

Plugin

A plugin is a unit of extension you install in Claude Code. Each plugin can ship any combination of:

• Skills (knowledge)
• Agents (specialized assistants)
• MCP servers (external integrations)
• Hooks (scripts that run on events)

Plugins are installed from a marketplace and live in your Claude Code config. They can be enabled or disabled globally, or scoped to a project if you want a plugin only in a specific folder.

When you install a plugin, all four kinds of things it bundles become available, and they show up in their respective sidebar sections in CLACOROO.

CLACOROO section: Plugins.

Skill

A skill is a piece of context Claude Code loads on demand. Concretely, a skill is a Markdown file with a description of when it applies — when you (or another tool) mention something that matches, Claude Code adds the skill’s content to the prompt.

Skills are passive: they don’t run code, they don’t have tools. They teach the assistant how to think about a specific topic (write a SQL migration, format JSON for a specific API, follow a style guide, …).

CLACOROO section: Skills — explore, preview, copy the trigger pattern, edit.

Agent

An agent is a specialized assistant Claude Code can delegate to. An agent has its own:

• System prompt (the instructions it’s launched with)
• Tool list (Bash, Edit, Read, Write, WebFetch, …)
• Scope (the kind of task it handles)

You launch an agent explicitly (with /agent-name or similar) when you want a specialised behavior — like “act as a code reviewer”, “act as a release notes writer”, “act as an accessibility auditor”.

Agents are active: they run, they call tools, they produce results.

CLACOROO section: Agents — explore, read the launch command, see which tools they have.

MCP server

A Model Context Protocol (MCP) server is the bridge between Claude Code and an external tool. Through an MCP server, the assistant can query a database, hit an API, search a docs index, run a search-on-vector-store — anything the server is wired to do.

MCP servers come in three transports:

• http — HTTPS request/response
• sse — server-sent events (streaming HTTP)
• stdio — local subprocess CLACOROO talks to over standard input/output

CLACOROO section: MCP servers — see status (Connected · Needs Auth · Error), add/remove user-added servers.

Hook

A hook is a script Claude Code runs at a specific moment. Plugins declare hooks to add behavior at events like:

• PreToolUse — before a tool runs
• PostToolUse — after a tool runs
• UserPromptSubmit — when you send a message
• SessionStart — at session start
• Stop — when the assistant stops

Hooks are automatic — you don’t invoke them. They fire on their events, run their command, and (if they’re well-written) silently improve your workflow.

CLACOROO section: Hooks — see every hook grouped by event, with their plugin and CLI dependencies.

At a glance

Object	What it is	How it’s triggered	CLACOROO section
Marketplace	The source of plugins	You add it	Marketplaces
Plugin	The installable unit	You install/enable/disable it	Plugins
Skill	A context file loaded on demand	Pattern match in conversation	Skills
Agent	A specialised assistant	You launch it explicitly	Agents
MCP server	A bridge to an external tool	Claude Code uses it when needed	MCP servers
Hook	A script run on an event	Fires automatically on its event	Hooks

Two more things to know

Scopes

Plugins (and MCP servers) can be scoped:

• Global — active in every Claude Code session
• Project — active only inside a specific folder
• Local — same idea, in some places used as a synonym for project

CLACOROO shows the scope as a badge on each card and lets you filter by it.

Where it all lives on disk

All your Claude Code configuration is on disk in plain files, mostly in:

• ~/.claude/ (macOS, Linux)
• %APPDATA%\Claude\ (Windows)

CLACOROO reads from there and writes only the files it has to (mostly settings.json). The rest is mediated by claude ... commands.

Where to go next

• Plugins — the workhorse section: enable, disable, update, remove
• MCP servers — wire up your first integration
• Hooks — discover what fires when and what it depends on
• Quick start — the five-minute walkthrough that turns these concepts into actions