Plugins, Connectors, and Marketplaces

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What are all these things?

Every product lets you add things to a coding agent or AI app, but each product uses its own names and the same word can mean different things. Every one of them is one of five kinds of thing: tools, instructions, hooks, packages and marketplaces.

Claude apps means claude.ai and the Claude Desktop app. An Accidental Guide to: Agents, Harnesses, Skills, and Tools explains the basic terms.

The map

Each colored line is one kind of thing, and each stop is a name you’ll see.

line To | Tools: reach other systems | MCP server, Desktop extension, Extension
line In | Instructions: how to work | Instructions file, Skill, Slash command, Prompt file, Agent definition
line Hk | Hooks: run at set moments | Hook
line Pl | Packages: install in one step | Extension, Plugin
line Mk | Marketplaces: lists to install from | Marketplace, Directory, MCP registry
station MCP server | 0 0 | r
also MCP server | Connector | Claude apps
also MCP server | App | ChatGPT, Codex
station Desktop extension | 0 1.8 | r
also Desktop extension | Local connector | Claude apps
station Extension | 0.8 3.6 | br
station Instructions file | 4 0 | l
also Instructions file | Project instructions | Claude apps
station Skill | 4 1.1 | l
station Slash command | 4 2.2 | l
also Slash command | Command | Claude Code
station Prompt file | 4 3.3 | l
also Prompt file | Custom prompt | Codex, deprecated
station Agent definition | 3.6 4.9 | l
also Agent definition | Custom agent | Copilot, VS Code, Visual Studio
also Agent definition | Subagent | Claude Code, Codex
station Hook | 1.2 5.5 | r
station Plugin | 2 3.6 | b
also Plugin | Agent plugin | VS Code
station Marketplace | 0 7 | ar
also Marketplace | Visual Studio Marketplace | editor extensions
also Marketplace | Claude Marketplace | a website
station Directory | 2 7 | b
also Directory | Connectors Directory | Claude apps
station MCP registry | 4 7 | al

Tip

Find a new word on its line, then check the product because names can overlap.

01 Tools

Field	Text
What	Most tools you add come from MCP servers, which some products call connectors, apps or extensions. See An Accidental Guide to: Agents, Harnesses, Skills, and Tools.
So what	One MCP server works in all these products, so ask for one when the agent needs a new system. See An Accidental Guide to: Model Context Protocol.

Names

Name	What it is
MCP server	A program that gives the agent tools
Connector	What Claude apps call an MCP server. OpenAI says app.
Desktop extension	A local MCP server in one file, for Claude Desktop
Extension	A tool module in Copilot CLI, or a VS Code add-on that adds tools

Confused with: Instructions

A tool reaches another system. Instructions say when to use it.

02 Instructions

Field	Text
What	Instructions tell the agent how to work. An instructions file loads every session. See An Accidental Guide to: Agents, Harnesses, Skills, and Tools.
So what	Put rules in an instructions file. Steps for one kind of task go in a skill, which loads only when a task needs it. See An Accidental Guide to: Agent Skills.

Names

Name	What it is
Instructions file	Read every session, such as AGENTS.md or CLAUDE.md. Claude apps say project instructions.
Skill	Loaded when the task matches or when you type /name
Prompt file	A saved prompt you run with /name
Custom agent	Sets up a sub-agent. Claude Code and Codex say subagent.

Confused with: Hooks

Instructions guide the model. A hook runs every time, even if the model skips an instruction.

03 Hooks

Field	Text
What	A hook is a command the harness runs at a set moment, such as after every edit. The model does not choose whether it runs.
So what	Use a hook for anything that must happen every time. A check before each commit is one example.

Names

Name	What it is
Hook	A command the harness runs on an event
Hook	In Claude apps, only inside a plugin, in Cowork

Confused with: Tools

A tool runs when the model calls it. A hook runs when its event happens.

04 Packages

Field	Text
What	A plugin is a package of skills, agent definitions, hooks and MCP servers. You install it in one step.
So what	Copilot CLI, VS Code and Codex read Claude Code’s plugin files. Each loads only the parts it supports.

Names

Name	What it is
Plugin	A folder of agent parts installed as one package
Agent plugin	VS Code’s name for a plugin
Extension	An add-on for the VS Code or Visual Studio editor
IDE extension	Claude Code or Codex itself, inside the editor

Confused with: Marketplaces

A plugin is a package you install. A marketplace tells your product where to find it.

05 Marketplaces

Field	Text
What	A plugin marketplace is a marketplace.json catalog in a Git repository. Add it, then install plugins by name.
So what	Anyone can publish a marketplace, so adding one means trusting whoever runs it. Anthropic reviews the plugins in its directory, but not ones added from a marketplace.

Names

Name	What it is
Marketplace	A list of plugins kept in a Git repository
Directory	A list the company reviews, such as the Connectors Directory
MCP registry	GitHub’s list of MCP servers
Visual Studio Marketplace	The store for VS Code and Visual Studio extensions

Confused with: Visual Studio Marketplace

The Visual Studio Marketplace is a store for editor extensions, and Claude Marketplace is a website. Neither one is a plugin marketplace.

Which product uses which word

These are the words each product uses, and what they mean there, as of October 2026. No means the product’s documentation doesn’t use the word.

Word	Claude Code	Claude apps	Copilot CLI	VS Code	Visual Studio	Codex
MCP server	yes	as connector	yes	yes	yes	yes
Connector	from claude.ai	MCP server	no	no	no	inside plugins
Extension	harness in an editor	local MCP server	tool module	editor add-on	editor add-on	harness in an editor
Instructions file	CLAUDE.md	project instructions	yes	yes	yes	AGENTS.md
Prompt file	merged into skills	no	no	Local harness only	yes	deprecated
Custom agent	subagent	Cowork only	yes	yes	yes	subagent
Hook	yes	Cowork only	yes	preview	no	yes
Plugin	yes	yes	yes	agent plugin	no	not in the IDE
Marketplace	plugin list	plugin list	plugin list	both kinds	extension store	plugin list

Each product has its own guide: An Accidental Guide to: Claude Code, An Accidental Guide to: Claude Desktop, An Accidental Guide to: GitHub Copilot CLI, An Accidental Guide to: OpenAI Codex, and An Accidental Guide to: VS Code and Visual Studio.

Sources

These public sources were checked in October 2026.

Source	Date	Address
Anthropic, Claude Code: plugins	October 2026	code.claude.com/docs/en/plugins
Anthropic, Claude: plugins	October 2026	claude.com/docs/plugins/overview
Anthropic, Claude: connectors	October 2026	claude.com/docs/connectors
GitHub, Plugins for GitHub Copilot	October 2026	docs.github.com/en/copilot/concepts/customizations/plugins
Microsoft, Agent plugins in VS Code	October 2026	code.visualstudio.com/docs/agent-customization/agent-plugins
Microsoft, Use MCP servers to extend GitHub Copilot in Visual Studio	October 2026	learn.microsoft.com/en-us/visualstudio/ide/mcp-servers
OpenAI, Plugins	October 2026	learn.chatgpt.com/docs/plugins
OpenAI, Plugin controls	October 2026	learn.chatgpt.com/docs/enterprise/apps-and-connectors