How It Works
Claude Code is powerful out of the box. But without extensions, it starts every conversation from scratch — no memory of your stack, your conventions, or the tools you use every day.
Extensions change that. They give Claude persistent knowledge about your workflows, automatic guardrails that run without prompting, direct access to your tools and databases, and project context that carries across every session. Four building blocks make this work:
Why extend Claude Code?
Without extensions
- Explain your coding style every conversation
- Manually copy configs from docs
- No access to your database or APIs
- Repeat multi-step workflows from scratch
- No guardrails — hope Claude follows your rules
With extensions
- Claude already knows your conventions
- One-click install for any MCP server
- Query databases, manage PRs, send messages directly
- Invoke complex workflows with a slash command
- Hooks auto-format, lint, and notify on every action
Skills
SkillWhat Claude knows how to do
What it is
A skill is a set of instructions — packaged as a Markdown file or folder — that teaches Claude how to handle a specific task. When you invoke a skill as a slash command like /review or /deploy, Claude follows those instructions step by step.
Why you need it
Without skills, you re-explain your process every time. "Review this code using our team's checklist" becomes a paragraph-long prompt. With a skill, it's just /review. Skills also ensure consistency — every team member gets the same workflow, not a different interpretation of a vague prompt.
How it works
Skills follow Anthropic's official format — a folder with a SKILL.md file and optional bundled scripts, references, and assets:
my-skill/ ├── SKILL.md # Required — instructions + YAML frontmatter ├── scripts/ # Optional — executable code ├── references/ # Optional — docs loaded on demand └── assets/ # Optional — templates, icons, etc.
Simple skills can be a single SKILL.md file. Folder-based skills can be downloaded as a zip from claudemcp.io.
Examples
- Code review with your team's standards
- Generate test suites matching your patterns
- Set up AWS infrastructure, Stripe billing, or Docker from scratch
- Meta Ads or Google Ads campaign builder
- SEO audit and fix for any website
Stored in .claude/commands/ (project) or ~/.claude/commands/ (global).
Hooks
HookWhat happens automatically
What it is
Hooks are event-driven automations. They run shell commands automatically in response to Claude Code events — like after a file is written, before a command runs, or when a conversation starts.
Why you need it
Hooks are your safety net. Instead of remembering to run Prettier after every edit or checking that Claude doesn't modify protected files, hooks handle it automatically. They enforce guardrails without you having to ask — every time, without exception.
How it works
Hooks are JSON configurations in your settings file. Each hook specifies an event (like PostToolUse), a file matcher pattern, and a shell command to run. Claude Code executes the command automatically when the event fires.
Examples
- Auto-format files with Prettier after every edit
- Run linters before Claude commits code
- Send a desktop or iMessage notification when a long task finishes
- Block writes to protected files
Configured in .claude/settings.json (project) or ~/.claude/settings.json (global).
MCP Servers
MCP ConfigWhat Claude can connect to
What it is
MCP (Model Context Protocol) servers connect Claude to external tools and data sources. Each config tells Claude Code how to launch and communicate with a server — giving Claude live access to databases, APIs, browsers, and third-party services.
Why you need it
Without MCPs, Claude can only read and write files. With them, it becomes part of your entire stack — querying your database, managing GitHub issues, sending Slack messages, pulling analytics, and controlling browsers. MCPs are what turn Claude from a code assistant into a full development partner.
How it works
MCP configs are JSON objects that specify a server command and its arguments. Add them to your .claude/mcp.json file, or use the CLI:
claude mcp add github -- npx -y @modelcontextprotocol/server-github
Examples
- GitHub — manage repos, PRs, and issues
- PostgreSQL — query and inspect your database
- Slack — read and send messages
- Shopify — manage products, orders, and inventory
- Stripe — read customers, subscriptions, and invoices
Configured in .claude/mcp.json under mcpServers. Restart Claude Code after adding.
CLAUDE.md
CLAUDE.mdWhat Claude knows about your project
What it is
CLAUDE.md is a project-level instruction file that Claude reads automatically at the start of every conversation. It defines your coding conventions, project structure, architectural decisions, and any rules Claude should follow.
Why you need it
Without CLAUDE.md, you repeat yourself every session: "use TypeScript strict mode", "put API routes in app/api/", "we use Tailwind, not CSS modules." With CLAUDE.md, you write it once and Claude always knows. It's the difference between onboarding a new developer every morning and working with someone who already knows the codebase.
How it works
Create a CLAUDE.mdfile in your project root. Claude reads it automatically — no configuration needed. Include your tech stack, file structure, naming conventions, testing requirements, and anything else you'd tell a new team member on day one.
Examples
- Next.js project with TypeScript, Tailwind, and Prisma conventions
- Python API with FastAPI patterns and testing requirements
- Godot 4 game project with GDScript and scene organization
- Full-stack SaaS with auth, billing, and deployment rules
Saved as CLAUDE.md in your project root, or ~/.claude/CLAUDE.md for global instructions.
Start with one
The fastest way to see the value is to add a single MCP server. Pick one, run the CLI command, and watch Claude connect to your tools in 30 seconds.