Claude Code - Complete Guide to AI-Powered Coding Assistant

Claude Code is Anthropic’s official AI coding assistant that runs in your terminal. It’s a powerful tool that can read your codebase, write code, execute commands, and help you build software faster than ever before.

What is Claude Code?

Claude Code is a command-line tool that brings Claude’s intelligence directly into your development workflow. Unlike traditional AI chat interfaces, Claude Code has direct access to your files, can run terminal commands, and understands your entire project context.

Key Features

• Code Understanding: Reads and understands your entire codebase
• File Operations: Creates, modifies, and deletes files
• Terminal Access: Executes shell commands safely
• Memory System: Remembers project context across sessions
• Skills: Reusable workflows and best practices
• Subagents: Specialized AI assistants for different tasks
• MCP Integration: Connect to external tools and APIs

Architecture Overview

The diagram above shows how Claude Code processes user input through its tool system, interacts with local files and MCP servers, and uses memory (CLAUDE.md) to maintain context.

Prerequisites

Before installing Claude Code, you need the following:

Requirement	Description
Node.js	Version 18.0 or higher
npm	Comes with Node.js
Anthropic API Key	Get from console.anthropic.com

Installation by Operating System

Windows Installation

Step 1: Install Node.js

Option A: Using Official Installer (Recommended)

1. Download Node.js from nodejs.org
2. Choose the LTS (Long Term Support) version
3. Run the installer and follow the prompts
4. Verify installation:

node --version
npm --version

Option B: Using Chocolatey Package Manager

# Install Chocolatey (if not installed)
Set-ExecutionPolicy Bypass -Scope Process -Force; [System.Net.ServicePointManager]::SecurityProtocol = [System.Net.ServicePointManager]::SecurityProtocol -bor 3072; iex ((New-Object System.Net.WebClient).DownloadString('https://community.chocolatey.org/install.ps1'))

# Install Node.js
choco install nodejs-lts -y

# Verify installation
node --version
npm --version

Option C: Using winget (Windows Package Manager)

winget install OpenJS.NodeJS.LTS

# Restart your terminal, then verify
node --version
npm --version

Step 2: Install Claude Code

npm install -g @anthropic-ai/claude-code

Step 3: Authenticate

claude
# Follow the prompts to authenticate with your Anthropic account

macOS Installation

Step 1: Install Node.js

Option A: Using Homebrew (Recommended)

# Install Homebrew (if not installed)
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

# Install Node.js
brew install node

# Verify installation
node --version
npm --version

Option B: Using Official Installer

1. Download Node.js from nodejs.org
2. Choose the macOS installer
3. Run the installer and follow the prompts
4. Verify installation:

node --version
npm --version

Option C: Using nvm (Node Version Manager)

# Install nvm
curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.0/install.sh | bash

# Restart your terminal, then install Node.js
nvm install --lts
nvm use --lts

# Verify installation
node --version
npm --version

Step 2: Install Claude Code

npm install -g @anthropic-ai/claude-code

Step 3: Authenticate

claude
# Follow the prompts to authenticate with your Anthropic account

Linux Installation

Ubuntu/Debian (Fresh Installation)

For a fresh Ubuntu system, follow these steps from scratch:

Step 1: Update System Packages

sudo apt update && sudo apt upgrade -y

Step 2: Install Essential Build Tools

sudo apt install -y build-essential curl wget git

Step 3: Install Node.js

Option A: Using NodeSource Repository (Recommended)

# Add NodeSource repository for Node.js 20 LTS
curl -fsSL https://deb.nodesource.com/setup_20.x | sudo -E bash -

# Install Node.js
sudo apt install -y nodejs

# Verify installation
node --version
npm --version

Option B: Using nvm (Node Version Manager)

# Install nvm
curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.0/install.sh | bash

# Reload shell configuration
source ~/.bashrc

# Install Node.js LTS
nvm install --lts
nvm use --lts

# Verify installation
node --version
npm --version

Option C: Using Ubuntu Repository (Older Version)

# Note: Ubuntu repository may have older Node.js version
sudo apt install -y nodejs npm

# You may need to update npm
sudo npm install -g npm@latest

# Verify installation
node --version
npm --version

Step 4: Fix npm Permissions (Optional but Recommended)

If you get permission errors when installing global packages:

# Create directory for global packages
mkdir ~/.npm-global

# Configure npm to use new directory
npm config set prefix '~/.npm-global'

# Add to your shell profile
echo 'export PATH=~/.npm-global/bin:$PATH' >> ~/.bashrc
source ~/.bashrc

Step 5: Install Claude Code

npm install -g @anthropic-ai/claude-code

Step 6: Authenticate

claude
# Follow the prompts to authenticate with your Anthropic account

Fedora/RHEL/CentOS

Step 1: Install Node.js

# For Fedora
sudo dnf install -y nodejs npm

# For RHEL/CentOS (with EPEL)
sudo dnf install -y epel-release
sudo dnf install -y nodejs npm

# Verify installation
node --version
npm --version

Step 2: Install Claude Code

npm install -g @anthropic-ai/claude-code

Arch Linux

# Install Node.js
sudo pacman -S nodejs npm

# Verify installation
node --version
npm --version

# Install Claude Code
npm install -g @anthropic-ai/claude-code

WSL (Windows Subsystem for Linux) Installation

Step 1: Install WSL

# Run in PowerShell as Administrator
wsl --install

# Restart your computer if prompted

Step 2: Install Ubuntu from Microsoft Store

Or use the command:

wsl --install -d Ubuntu

Step 3: Follow Ubuntu Installation Steps

Open your WSL Ubuntu terminal and follow the Ubuntu/Debian installation steps above.

Authentication Methods

Method 1: Interactive Login (Recommended)

claude
# Follow the prompts to log in via browser

Method 2: API Key

# Set environment variable
export ANTHROPIC_API_KEY=your-api-key-here

# Or add to your shell profile
echo 'export ANTHROPIC_API_KEY=your-api-key-here' >> ~/.bashrc
source ~/.bashrc

Method 3: Configuration File

Create ~/.claude/config.json:

{
  "apiKey": "your-api-key-here"
}

Basic Usage

cd your-project
claude

This starts an interactive session where you can ask Claude to help with your code.

First-Time Setup

When you run Claude Code for the first time:

1. Authentication: You’ll be prompted to authenticate
2. Permissions: Grant necessary permissions
3. Project Setup: Run /init to create project memory

# Initialize project memory
/init

# Check status
/status

Troubleshooting Installation Issues

“command not found: claude”

Solution:

# Check if npm global bin is in PATH
npm config get prefix

# Add to PATH (add to ~/.bashrc or ~/.zshrc)
export PATH="$(npm config get prefix)/bin:$PATH"

# Reload shell
source ~/.bashrc  # or source ~/.zshrc

Permission Denied Errors

Solution:

# Option 1: Use sudo (not recommended)
sudo npm install -g @anthropic-ai/claude-code

# Option 2: Fix npm permissions (recommended)
mkdir ~/.npm-global
npm config set prefix '~/.npm-global'
echo 'export PATH=~/.npm-global/bin:$PATH' >> ~/.bashrc
source ~/.bashrc

# Reinstall
npm install -g @anthropic-ai/claude-code

Node.js Version Too Old

Solution:

# Using nvm
nvm install --lts
nvm use --lts

# Or update via package manager
# Ubuntu/Debian
curl -fsSL https://deb.nodesource.com/setup_20.x | sudo -E bash -
sudo apt install -y nodejs

Network/Proxy Issues

Solution:

# Configure npm proxy
npm config set proxy http://proxy-server:port
npm config set https-proxy http://proxy-server:port

# Or use a different registry
npm config set registry https://registry.npmmirror.com

Core Concepts

1. Slash Commands

Slash commands are shortcuts that control Claude’s behavior. Type / to see all available commands.

Essential Commands:

Command	Purpose
/help	Show available commands
/clear	Clear conversation
/model	Switch AI model
/memory	Edit project memory
/init	Initialize project memory

2. Memory (CLAUDE.md)

Memory allows Claude to retain context across sessions. Create a CLAUDE.md file in your project root:

# Project Configuration

## Tech Stack
- Node.js with TypeScript
- PostgreSQL database
- React frontend

## Coding Standards
- Use async/await over promises
- Prefer functional components
- Write tests for all new features

3. Skills

Skills are reusable capabilities that extend Claude’s functionality. They’re stored in .claude/skills/:

.claude/skills/
├── code-review/
│   └── SKILL.md
├── optimize/
│   └── SKILL.md
└── test-generator/
    └── SKILL.md

4. Subagents

Subagents are specialized AI assistants for specific tasks:

• Code Reviewer: Reviews code for quality and security
• Test Engineer: Generates and runs tests
• Documentation Writer: Creates documentation
• Debugger: Helps find and fix bugs

5. MCP (Model Context Protocol)

MCP connects Claude to external tools and APIs:

• GitHub integration
• Database access
• Slack notifications
• File system operations

Practical Examples

Example 1: Code Review

# Start Claude
claude

# Ask for a code review
> Review the authentication module for security issues

Example 2: Generate Tests

> Generate unit tests for the UserService class

Example 3: Refactor Code

> Refactor the API handlers to use async/await

Best Practices

1. Use Memory: Create a CLAUDE.md file with project context
2. Create Skills: Build reusable workflows for common tasks
3. Use Checkpoints: Save progress before major changes
4. Configure MCP: Connect to your tools and services
5. Review Changes: Always review Claude’s changes before committing

Learning Path

Level	Topic	Time
Beginner	Slash Commands	30 min
Beginner	Memory	45 min
Intermediate	Skills	1 hour
Intermediate	Hooks	1 hour
Advanced	MCP	1 hour
Advanced	Subagents	1.5 hours

Resources

• Official Documentation
• Claude How To Guide
• Anthropic API Reference

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This guide is part of our AI Development Tools series. Stay tuned for more detailed tutorials on each Claude Code feature.