Claude Code — Getting Started

Claude Code is Anthropic's terminal-based AI coding agent. It reads your codebase, writes and edits files, runs terminal commands, and can autonomously complete multi-step engineering tasks — all through natural language prompts in your terminal.

Installation

# Via npm (recommended)
npm install -g @anthropic-ai/claude-code

# Via Homebrew
brew install claude-code

# Verify installation
claude --version

Authentication

You need an Anthropic API key. Get one at console.anthropic.com (API Keys section).

# Set as environment variable
export ANTHROPIC_API_KEY="sk-ant-..."

# Or Claude Code will prompt on first run
claude

First Session

Navigate to your project directory and launch Claude Code:

cd my-project
claude

Claude Code scans your project structure automatically. On first run, you'll see:

⚡ Welcome to Claude Code!

  Directory: /Users/you/my-project
  Model: claude-sonnet-4-20250514 (default)
  Context: 200K tokens
  
  Type /help for available commands.
  
>

Type a prompt to start:

> Explain the architecture of this project and suggest improvements

Claude Code will read relevant files, analyze the structure, and respond inline in your terminal.

Essential Slash Commands

Project Configuration: CLAUDE.md

Create a CLAUDE.md file in your project root (or .claude/CLAUDE.md). Claude Code reads this every session — it's your project's system prompt.

# CLAUDE.md

## Commands
- `npm run dev` — Start development server
- `npm run build` — Production build
- `npm run lint` — ESLint + TypeScript check
- `npm run test` — Run test suite

## Architecture
- Next.js 14 App Router
- TypeScript strict mode
- Tailwind CSS for styling
- PostgreSQL via Prisma ORM

## Conventions
- Use server components by default
- `'use client'` only for interactivity
- Path alias `@/` maps to project root
- No any types — use explicit types or unknown

See Prompt Engineering in Claude Code for advanced CLAUDE.md patterns.

Environment Variables

Related Pages

• Prompt Engineering in Claude Code — CLAUDE.md patterns, extended thinking
• Claude Code Configuration Reference — claude.json, MCP, hooks, .claude/ conventions
• Tool Comparison — Claude Code vs OpenCode vs Gemini CLI vs Cursor vs Copilot
• Claude Code vs Gemini CLI vs OpenCode (Blog) — Head-to-head comparison
• Prompting Claude Code (Prompts Section) — Detailed CLAUDE.md command patterns
• MCP Setup for Claude Code — Adding MCP servers