How to Use Claude Code in 2026: Install, CLAUDE.md Setup, Slash Commands & Real Costs

If you've been using GitHub Copilot inside your IDE and wondering what all the Claude Code noise is about, here's the honest answer: Claude Code operates in a different lane entirely. It's not an autocomplete plugin — it's a terminal-based AI agent that reads your whole codebase, plans multi-step tasks, writes and edits files, runs tests, and can spin up specialized sub-agents to tackle work in parallel.

In 2026, Claude Code has become the default tool for developers who want an AI that actually understands what they're building rather than pattern-matching the current cursor position. This guide covers everything you need to go from zero to productive in under an hour.

What Is Claude Code (and How Is It Different from Copilot)?

GitHub Copilot lives inside your IDE and responds to your cursor. It sees the current file and some context, suggests completions, and answers questions in a chat panel. It's excellent at what it does.

Claude Code is a command-line agent that runs in your terminal. When you run claude in a project directory, it ingests your entire codebase structure, reads relevant files, and executes multi-step tasks autonomously. It can:

• Write, edit, and refactor code across multiple files in one command
• Run shell commands, tests, and builds
• Commit to git with meaningful messages
• Create and manage GitHub PRs via the gh CLI
• Spawn parallel sub-agents for independent tasks
• Use the Model Context Protocol (MCP) to connect external tools

The key distinction: Copilot helps you write code faster. Claude Code handles tasks while you do something else.

Step 1: Install Claude Code

Claude Code requires Node.js 18 or higher. Check your version with node --version. If you're below 18, update via nodejs.org or using a version manager like nvm.

Install Claude Code globally:

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

Once installed, set your Anthropic API key. Get one at console.anthropic.com — new accounts receive $5 in free credits, enough for meaningful experimentation.

export ANTHROPIC_API_KEY=sk-ant-your-key-here

Add that line to your ~/.bashrc or ~/.zshrc so it persists across sessions. Then verify:

claude --version
claude /doctor

/doctor runs a health check — it confirms your API connection, Node version, and tool availability. Fix anything it flags before proceeding.

Step 2: Your First Session

Navigate to a project directory and run:

claude

Claude Code opens an interactive session. It immediately reads your directory structure and notes key files. You can now give it natural language instructions:

• "Add input validation to the signup form"
• "Write tests for the AuthService class"
• "Refactor the database connection to use a connection pool"
• "Find all places we're logging user emails and remove them"

Claude Code will show you its plan, ask permission before editing files (in default mode), and execute step by step. You approve each tool call or run in a less-interrupted mode (see below).

For a single non-interactive command — useful for scripts and automation — use --print:

claude --print "Explain what this codebase does in 3 sentences"

Step 3: Set Up CLAUDE.md (The Most Important Step)

CLAUDE.md is a markdown file you place in your project root (or ~/.claude/CLAUDE.md for global rules). Claude Code reads it at the start of every session and treats it as authoritative instructions.

This is where Claude Code becomes dramatically more useful than a generic chat session. A well-written CLAUDE.md tells it:

• Tech stack and conventions — "We use TypeScript strict mode, Prisma for ORM, Jest for testing"
• Commands to know — "Run npm test for tests, npm run dev for local server"
• Coding standards — "Functions should be under 50 lines. No any types."
• What NOT to do — "Never modify migration files. Don't use console.log in production code."
• Architecture notes — "API routes live in /src/routes. Business logic in /src/services."

Example CLAUDE.md:

# Project: MyApp API

## Stack
- Node.js 20, TypeScript strict, Express 5
- PostgreSQL via Prisma ORM
- Jest + Supertest for tests
- Deployed to Railway

## Commands
- `npm test` — run test suite
- `npm run dev` — start dev server on :3000
- `npx prisma migrate dev` — apply DB migrations

## Conventions
- Controllers validate input; Services handle logic
- All DB queries go through the service layer
- Errors use the AppError class in /src/utils/errors.ts
- Never modify files in /src/generated/

With this file in place, Claude Code skips the "learn the codebase" phase and starts working immediately.

Step 4: Master the Slash Commands

Slash commands are entered during an interactive session. The ones worth memorizing:

Step 5: Permission Modes

Claude Code's default mode asks you to approve each file write and shell command. This is safe but interrupts flow. Three permission modes exist:

Default — Approves tool calls one by one. Good for sensitive codebases or when you want full control.

Auto (dontAsk) — Approves all non-destructive actions automatically. File writes, test runs, git operations proceed without prompts. Stops only for irreversible actions like force pushes.

Bypass — Approves everything. Use for automation, CI pipelines, or trusted scripts. Not recommended for interactive sessions.

Run with a specific mode:

claude --permission-mode dontAsk "Add error handling to all API routes"

For most developers, dontAsk mode becomes the daily driver once you trust the tool — it's fast without being reckless.

What Does Claude Code Actually Cost?

Claude Code uses your Anthropic API key, so you pay per token rather than a flat subscription. Real-world costs in 2026:

For comparison: GitHub Copilot Individual is $10/month, Copilot Business is $19/seat/month. If you're running 5–10 complex tasks per day, Claude Code's API costs can exceed Copilot's flat rate — but the capability difference justifies it for most teams. Light users (a few tasks per week) will spend well under $10/month.

Tip: Use Sonnet (the default) for most tasks. Switch to Opus only for the hardest problems — architecture planning, debugging gnarly production issues, or reviewing large pull requests.

Multi-Agent Mode: Where Claude Code Gets Powerful

For large tasks, Claude Code can spawn specialized sub-agents that work in parallel. This is available through the Agent tool in extended sessions. Common patterns:

• Researcher + Executor: One agent explores the codebase; another implements the change
• Writer + Reviewer: One agent writes code; another reviews it independently
• Parallel feature work: Two agents build two independent features simultaneously

To use this effectively, give Claude Code complex, open-ended tasks: "Audit this codebase for security vulnerabilities, then fix the top three findings" rather than step-by-step instructions. That's when the orchestration layer earns its keep.

Claude Code vs Cursor: Quick Take

Cursor is a full IDE fork (based on VS Code) with deep AI integration. It's excellent for developers who want AI inside their editor. Claude Code is better for developers who prefer their own editor setup and want an agent they can hand off tasks to completely. Many developers use both — Cursor for day-to-day coding, Claude Code for big refactors and automation.

Getting Started Today

The fastest path to productive:

1. npm install -g @anthropic-ai/claude-code
2. Add ANTHROPIC_API_KEY to your shell config
3. Create a CLAUDE.md in your project root
4. Run claude and give it one real task from your backlog

Most developers hit their first "this is different" moment within the first 20 minutes — usually when Claude Code reads five files, writes three more, runs the tests, and reports back with a complete solution while they were making coffee. That's the use case it was built for.