Claude Code Mastery: The Complete Guide to AI-Powered Development

Claude Code changed how I build software. What used to take weeks now takes hours. Not because it writes perfect code - it doesn't - but because it thinks alongside you, handling the tedious parts while you focus on architecture and product decisions.

This guide covers everything I've learned building 10+ production applications with Claude Code. From installation to advanced subagent workflows, this is the reference I wish I'd had when I started.

What Is Claude Code?

Claude Code is Anthropic's terminal-based AI coding assistant. Unlike ChatGPT or web-based tools, it runs in your terminal with direct access to your filesystem, git, and shell. It reads your codebase, writes code, runs commands, and iterates based on results.

Think of it as a senior developer pair-programming with you, but one that never gets tired and can process your entire codebase in seconds.

Key capabilities:

• Reads and writes files across your project
• Runs shell commands and interprets output
• Uses git for version control
• Supports subagents for parallel work
• Plan mode for complex architecture decisions
• Plugin system for extending functionality

Getting Started: Installation

Install Claude Code globally via npm:

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

Verify the installation:

claude --version

Set your API key:

export ANTHROPIC_API_KEY=your-key-here

Then navigate to any project directory and run:

claude

Claude Code will automatically detect your project structure, read configuration files, and understand your codebase.

The CLAUDE.md File: Your Project's Brain

Every project should have a CLAUDE.md file at the root. This is the instruction manual that Claude Code reads at the start of every session. Think of it as your project's personality file.

What to include:

• Project purpose and stack
• Key commands (npm run dev, npm run test)
• Architecture decisions and conventions
• File structure overview
• Common patterns to follow
• Things to avoid

# My Project

## Stack
Next.js 14, TypeScript, Tailwind, Supabase

## Commands
npm run dev      # Development
npm run build    # Production build
npm run test     # Run tests

## Conventions
- Use App Router (not Pages)
- Server Components by default
- Client Components only when needed (interactivity)
- Zod for all validation

The better your CLAUDE.md, the better Claude Code performs. I spend 15 minutes setting this up for every new project and it saves hours.

Plan Mode: Think Before You Code

Plan mode is Claude Code's most underrated feature. Instead of jumping straight into writing code, it explores your codebase, analyzes the problem, and presents an implementation plan for your approval.

When to use plan mode:

• New features that touch multiple files
• Architectural decisions with multiple valid approaches
• Refactoring that affects existing behavior
• Any task where you want to review the approach first

In plan mode, Claude Code uses read-only tools - Glob, Grep, Read - to understand your codebase before proposing changes. This prevents the "code first, think later" pattern that leads to messy implementations.

My workflow:

1. Describe what I want to build
2. Let Claude enter plan mode
3. Review the plan - check file paths, approach, trade-offs
4. Approve or adjust
5. Execute

This single practice has eliminated 80% of the "undo and redo" cycles I used to have.

Subagents: Parallel Work

Subagents let Claude Code spawn child processes that work independently. This is how you get 10x throughput on complex tasks.

Use cases:

• Research multiple files simultaneously
• Run tests while continuing development
• Explore different approaches in parallel
• Build infrastructure while writing business logic

Each subagent has its own context and can use the same tools as the main agent. Results flow back to the parent for synthesis.

Example: When building a new feature, I'll have Claude spawn three subagents:

1. One to research the existing codebase for patterns
2. One to explore the library documentation
3. One to design the data model

All three run simultaneously, and the main agent synthesizes their findings into an implementation plan.

Plugins and Skills

Claude Code's plugin system extends its capabilities with specialized skills. Plugins can define:

• Custom slash commands
• Specialized workflows
• Domain knowledge
• Tool integrations

Essential plugins I use:

• Test-driven development - Forces writing tests before implementation
• Git worktrees - Isolates feature work in separate directories
• Code review - Multi-pass review before committing
• Plan execution - Structured plan-then-execute workflow

Plugins live in your project's .claude/ directory or can be installed globally.

Real Workflows: How I Build

Starting a new feature

1. Write a clear description of what I want
2. Claude enters plan mode, explores the codebase
3. I review and approve the plan
4. Claude executes, creating files, writing tests, running builds
5. I review the output, request adjustments
6. Final verification - does it build? Do tests pass?

Debugging

1. Describe the bug or paste the error
2. Claude reads relevant files, traces the issue
3. Proposes a fix with explanation
4. I approve, Claude implements and verifies

Refactoring

1. Describe what I want to change and why
2. Claude analyzes impact - what files are affected?
3. Plan mode shows the full scope of changes
4. Incremental execution with verification at each step

Cost Management

Claude Code runs on API credits. Here's how I manage costs:

• Use plan mode - Cheaper to think than to redo
• Be specific - Vague prompts waste tokens on exploration
• Batch work - Group related changes into sessions
• Use CLAUDE.md - Reduces repeated context-gathering

Typical costs for my workflow: $5-15/day for active development, much less for light usage.

Common Mistakes to Avoid

1. No CLAUDE.md - Claude Code works blind without project context
2. Skipping plan mode - Leads to implementations that don't fit your architecture
3. Vague prompts - "Make it better" wastes tokens. Be specific about what and why
4. Not reviewing output - Claude Code is capable but not infallible. Always review
5. Ignoring test failures - If tests fail, the code isn't done. Period

What's Next

Claude Code is evolving rapidly. Recent additions include:

• Enhanced subagent coordination
• Better plan mode with deeper codebase analysis
• Plugin marketplace
• MCP (Model Context Protocol) integrations

The developers building with these tools now will have a massive advantage as AI-assisted development becomes the norm.

Frequently Asked Questions

Is Claude Code free?

Claude Code vs Cursor - which should I use?

Can Claude Code write entire applications?

How do I install Claude Code?

What programming languages does Claude Code support?