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Chapter 01 · Section II · 15 min read

Installing and your first session

Twenty minutes of setup and you are talking to a working coding assistant inside your terminal. No IDE plugin needed. Node, an API key, and a shell.

Claude Code is distributed as a Node package. If you have a working Node install and an Anthropic account, you can be in a session in about five minutes. The rest of this section walks you through the steps — install, authenticate, launch, and quit — so nothing surprises you the first time.

Prerequisites

You need three things.

  1. Node.js 20 or later. If you already have a Node version manager like fnm or nvm, you can use that. If not, install from nodejs.org or via your package manager.
  2. An Anthropic API key. Sign up at console.anthropic.com, add a small amount of credit (or use free trial credit), and create an API key. Keep it somewhere safe.
  3. A terminal. Any modern terminal on macOS, Linux, or WSL on Windows works.

Install

The recommended way is via npm:

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

That drops a claude binary on your $PATH. Verify it worked:

claude --version

Authenticate

The first time you run the binary, it will walk you through authentication. Two options:

  1. Console login (recommended). Opens a browser window; you sign in with the same Anthropic account you use for console.anthropic.com. The token is saved in a config file in your home directory.
  2. API key. If you cannot open a browser (say, you are on a remote server), you can export ANTHROPIC_API_KEY in your shell profile instead.

Either way, this is a once-per-machine step.

Your first session

Change into a project directory — any project will do — and run:

claude

You are now in a session. The prompt is a simple text input. Try:

what files are in this repo?

Claude will probably use its Bash or Glob tool to answer. The first time it wants to run a shell command it will ask you for permission; approve it and you will see the output come back into the transcript.

Try one more:

open src/index.ts and summarise what it does

If the file exists, you will get a plain-English summary. If not, Claude will say so — it does not invent files.

Ending a session

Type /exit or hit Ctrl-C twice. Your conversation transcript is saved locally by default; you can review or resume it later. If you set up an IDE integration, sessions can persist across restarts too — but for this course we stick to the plain terminal.

Check your understanding

Quick check

—

Which of the following is the minimum you need to start a Claude Code session on a fresh laptop?