Understanding Claude Code — Your AI Engineering Partner

What Is Claude Code?

Claude Code is Anthropic's official command-line interface for Claude. But calling it a "CLI" dramatically undersells what it does. Claude Code is an agentic software engineering tool that operates directly in your development environment.

Think of it this way: ChatGPT and Claude.ai are like having a brilliant colleague you can message. Claude Code is like having that colleague sitting at your desk, with access to your files, your terminal, and your entire project.

How Claude Code Works

When you launch Claude Code in a project directory, it:

1. Reads your codebase — It can explore files, search for patterns, and understand your project structure
2. Understands context — Through CLAUDE.md files, it learns your conventions, architecture, and preferences
3. Makes changes — It edits files, creates new ones, and coordinates multi-file modifications
4. Runs commands — It executes tests, builds, linting, git operations, and any terminal command
5. Iterates autonomously — It can run tests, see failures, fix them, and re-run until everything passes

Core Capabilities

# Start Claude Code in any project
claude

# Give it a task
> Add user authentication with email/password and Google OAuth.
  Include login, register, forgot password, and email verification.
  Use the existing User model and follow the patterns in AuthController.

# Claude Code will:
# 1. Read your existing code and patterns
# 2. Plan the implementation
# 3. Create/modify multiple files
# 4. Run tests to verify
# 5. Fix any issues found

The CLAUDE.md File — Your Project's AI Instructions

The most powerful feature of Claude Code is the CLAUDE.md file. This is a Markdown file at your project root that tells Claude Code everything about your project:

# CLAUDE.md

## Tech Stack
- Next.js 15 with App Router
- PostgreSQL with Prisma ORM
- Tailwind CSS with shadcn/ui
- Stripe for billing

## Conventions
- Use TypeScript strict mode
- Server Components by default, Client Components only when needed
- All API routes return { data, error } shape
- Use Zod for validation

## Commands
- npm run dev — Start development server
- npm run test — Run Vitest tests
- npm run lint — ESLint check

When Claude Code reads this file, it follows your conventions automatically. No more explaining your preferences in every prompt.

Claude Code vs Traditional AI Assistants

MCP Servers — Extending Claude Code

Model Context Protocol (MCP) servers extend Claude Code with external capabilities:

• Database access — Query your database directly during development
• Documentation search — Pull in framework docs in real-time
• Browser automation — Test your UI with Playwright
• API testing — Hit your endpoints and verify responses

Practical Exercise

1. Install Claude Code: npm install -g @anthropic-ai/claude-code
2. Navigate to any existing project
3. Create a CLAUDE.md describing your project
4. Run claude and ask it to explain your project structure
5. Ask it to add a small feature and observe how it works

Key Takeaways

• Claude Code is an agentic tool that operates in your terminal with full project access
• The CLAUDE.md file is your most powerful tool for guiding AI behavior
• MCP servers extend Claude Code's capabilities beyond code editing
• The workflow shifts from writing code to directing and reviewing architecture