What Claude Code is

Not a completer, not a chat window

Autocomplete guesses the next few tokens at your cursor. It never sees whether the guess works. A chat window answers from what you pasted into it, and you carry the result back to your project by hand.

Claude Code sits somewhere else. It runs in your project, reads the files it needs, edits them, runs commands, and reads what those commands printed. You give it a goal in plain language, and it works toward it while you watch.

The practical consequence is that your job changes. You stop being the person who copies text between a chat and an editor. You become the person who states the goal, sets the limits, and judges the result.

What it can touch

Inside a session, Claude works through a small set of kinds of action, and the permission system is organised around them. Reading files inside the working directory needs no approval. Running shell commands needs approval, apart from a built-in set of read-only ones. Editing files is approved separately.

That split tells you what the tool really is: a program that can change your machine, with a gate in front of every change. The next lessons are mostly about that gate and about how to use it well.

Where it runs

The terminal is where it starts: you open a repository and run claude. But it is not only a terminal tool. The docs list the same agent in VS Code and JetBrains, in a Desktop app, on the web as cloud sessions, in Slack, with a Chrome integration, and on mobile.

You can also move a session between them. /teleport pulls a cloud session into your terminal, /desktop continues in the Desktop app, and /remote-control exposes the running session to claude.ai.

One more mode matters for scripts. claude -p "prompt" runs once without a conversation, and you can pipe input in:

For unattended runs the guide asks five questions before you leave: does it know what done is, can it check itself, what may it touch, what stops it, and who signs off.

Your own judgment versus enforcement

The most useful idea in the official guide is a distinction. Some things are Claude's judgment: prompts, CLAUDE.md, and the auto-mode classifier. Some things are enforced by the harness: hooks, deny rules, the sandbox, and tests.

Use the second kind only for rules with no exceptions, and do not expect the first kind to hold under pressure. "Never push to main" written in CLAUDE.md is a request. The same line as a deny rule is a wall.