Extend Claude Code

Claude Code combines a model that reasons about your code with built-in tools for file operations, search, execution, and web access. The built-in tools cover most coding tasks. This guide covers the extension layer: features you add to customize what Claude knows, connect it to external services, and automate workflows.

For how the core agentic loop works, see How Claude Code works.

New to Claude Code? Start with CLAUDE.md for project conventions, then add other extensions as specific triggers come up.

Overview

Extensions plug into different parts of the agentic loop:

CLAUDE.md adds persistent context Claude sees every session
Skills add reusable knowledge and invocable workflows
Code intelligence connects Claude to a language server for symbol-level navigation and live type errors
MCP connects Claude to external services and tools
Subagents run their own loops in isolated context, returning summaries
Agent teams coordinate multiple independent sessions with peer-to-peer messaging, plus a shared task list for agents that have the Task tools
Hooks run your script, HTTP request, prompt, or subagent when Claude Code reaches a lifecycle event
Plugins and marketplaces package and distribute these features

Skills are the most flexible extension. A skill is a markdown file containing knowledge, workflows, or instructions. You can invoke skills with a command like /deploy, or Claude can load them automatically when relevant. Skills can run in your current conversation or in an isolated context via subagents.

Match features to your goal

Features range from always-on context that Claude sees every session, to on-demand capabilities you or Claude can invoke, to background automation that runs on specific events. The table below shows what’s available and when each one makes sense.

Feature	What it does	When to use it	Example
CLAUDE.md	Persistent context loaded every conversation	Project conventions, “always do X” rules	”Use pnpm, not npm. Run tests before committing.”
Skill	Instructions, knowledge, and workflows Claude can use	Reusable content, reference docs, repeatable tasks	`/deploy` runs your deployment checklist; API docs skill with endpoint patterns
Subagent	Isolated execution context that returns summarized results	Context isolation, parallel tasks, specialized workers	Research task that reads many files but returns only key findings
Agent teams	Coordinate multiple independent Claude Code sessions	Parallel research, new feature development, debugging with competing hypotheses	Spawn reviewers to check security, performance, and tests simultaneously
Code intelligence	Language-server navigation and diagnostics	Typed languages, large codebases where grep is slow or imprecise	Jump to a symbol’s definition instead of reading the whole file
MCP	Connect to external services	External data or actions	Query your database, post to Slack, control a browser
Hook	Script, HTTP request, prompt, or subagent triggered by events	Automation that must run on every matching event	Run ESLint after every file edit
Artifact	Publish session output as a private, interactive web page	Output you want to see or share visually rather than as terminal text	An incident timeline that updates as Claude investigates

Plugins are the packaging layer. A plugin bundles skills, hooks, subagents, and MCP servers into a single installable unit. Plugin skills are namespaced (like /my-plugin:review) so multiple plugins can coexist. Use plugins when you want to reuse the same setup across multiple repositories or distribute to others via a marketplace.

Build your setup over time

You don’t need to configure everything up front. Each feature has a recognizable trigger, and most teams add them in roughly this order:

Trigger	Add
Claude gets a convention or command wrong twice	Add it to CLAUDE.md
You keep typing the same prompt to start a task	Save it as a user-invocable skill
You paste the same playbook or multi-step procedure into chat for the third time	Capture it as a skill
You keep copying data from a browser tab Claude can’t see	Connect that system as an MCP server
Claude reads many files to find where a symbol is defined or used	Install a code intelligence plugin for your language
A side task floods your conversation with output you won’t reference again	Route it through a subagent
You want something to happen every time without asking	Write a hook
A second repository needs the same setup	Package it as a plugin

The same triggers tell you when to update what you already have. A repeated mistake or a recurring review comment is a CLAUDE.md edit, not a one-off correction in chat. A workflow you keep tweaking by hand is a skill that needs another revision.

Compare similar features

Some features can seem similar. For a deeper walkthrough of choosing between them, see Steering Claude Code: when to use CLAUDE.md, skills, hooks, and subagents on the blog. Here’s how to tell them apart.

Skills and subagents solve different problems:

Skills are reusable content you can load into any context
Subagents are isolated workers that run separately from your main conversation

Aspect	Skill	Subagent
What it is	Reusable instructions, knowledge, or workflows	Isolated worker with its own context
Key benefit	Share content across contexts	Context isolation. Work happens separately, only summary returns
Context window impact	Adds to your main window	Uses a separate window with its own input and output tokens
Best for	Reference material, invocable workflows	Tasks that read many files, parallel work, specialized workers

Skills can be reference or action. Reference skills provide knowledge Claude uses throughout your session (like your API style guide). Action skills tell Claude to do something specific (like /deploy that runs your deployment workflow).Use a subagent when you need context isolation or when your context window is getting full. The subagent might read dozens of files or run extensive searches, but your main conversation only receives a summary. Since subagent work doesn’t consume your main context, this is also useful when you don’t need the intermediate work to remain visible. Custom subagents can have their own instructions and can preload skills.They can combine. A subagent can preload specific skills (skills: field). A skill can run in isolated context using context: fork. See Skills for details.

Getting started

Core concepts

Use Claude Code

Platforms and integrations

Overview

Match features to your goal

Build your setup over time

Compare similar features

​Overview

​Match features to your goal

​Build your setup over time

​Compare similar features

Overview

Match features to your goal

Build your setup over time

Compare similar features