Claude Code is the fastest-growing AI coding tool in the developer community. The r/ClaudeCode subreddit has 4,200+ weekly contributors — roughly 3x larger than r/Codex. Anthropic reports $2.5B+ in annualized revenue attributable to Claude Code adoption. This complete guide takes you from installation to your first productive agentic coding session.
What Is Claude Code?
Claude Code is a terminal-native AI coding tool from Anthropic. Unlike IDE plugins that assist line-by-line, Claude Code operates at the project level — it reads your entire codebase, understands the architecture, writes and edits multiple files in a single session, runs tests, and works through complex engineering tasks autonomously. It uses Claude models with a 1-million-token context window — large enough to hold an entire codebase in memory.
Installation
Requirements: Node.js 18+, a Claude Max subscription ($100+/month) or Anthropic API key.
# Install globally
npm install -g @anthropic-ai/claude-code
# Navigate to your project
cd your-project
# Authenticate
claude login
# Start a session
claudeSetting Up CLAUDE.md (The Most Important Step)
CLAUDE.md is a file you create in your project root that Claude Code reads at the start of every session. It’s the most important setup step — it gives Claude the context it needs to work effectively in your specific codebase without you re-explaining everything every time.
A good CLAUDE.md includes:
# Project: [Your Project Name]
## Architecture
[Brief description of how the codebase is organized]
## Tech Stack
- Language: [Python 3.11 / Node.js 20 / etc.]
- Framework: [Django / Next.js / etc.]
- Database: [PostgreSQL / MongoDB / etc.]
- Testing: [pytest / Jest / etc.]
## Coding Standards
- [Style guide, naming conventions, etc.]
- [Preferred patterns for this codebase]
## Common Tasks
- Run tests: `[command]`
- Start dev server: `[command]`
- Lint: `[command]`
## Known Issues / Context
- [Anything Claude should know before working]Key Slash Commands
| Command | What It Does |
|---|---|
| /init | Scans your codebase and generates an initial CLAUDE.md |
| /memory | View and edit Claude’s memory for this project |
| /compact | Compact the conversation to free up context space |
| /batch | Run multiple commands or edits in one operation |
| /clear | Clear conversation history (start fresh) |
Your First Agentic Session
Start Claude Code in your project directory and try:
- “Explain the overall architecture of this codebase” — Claude reads and summarizes
- “Add input validation to the user registration endpoint” — Claude finds the right file, writes the validation, updates tests
- “There’s a bug where [describe issue] — find it and fix it” — Claude searches the codebase, identifies the cause, fixes it
- “Write tests for [module or function]” — Claude reads the code and writes comprehensive tests
Rate Limits and Token Management
Claude Code on Max 5x gets approximately 44,000-220,000 tokens per 5-hour window. Long sessions with large codebases consume tokens quickly. Best practices:
- Use /compact when sessions get long to free up context
- Be specific in your requests — “fix the authentication bug in auth.py” uses fewer tokens than “look through all my files for problems”
- Auto-compaction (beta) handles this automatically when enabled
Frequently Asked Questions
What subscription do I need for Claude Code?
Claude Max at $100/month minimum. Claude Code can also be accessed via API billing — often more cost-effective for lower-volume use.
Can Claude Code edit multiple files at once?
Yes. Claude Code can read, edit, and create multiple files in a single session — and runs the edits atomically, so you can review and accept or reject changes.
How do I install Claude Code on Windows?
Claude Code requires Node.js 18+ and runs via WSL (Windows Subsystem for Linux) on Windows. Install WSL, then follow the standard npm installation steps within your WSL terminal.