What Is Claude Code? The Complete Guide

What is Claude Code? It is Anthropic's agentic coding tool: an AI agent that works in your terminal, IDE, or browser, reads your codebase, edits files, runs commands, and opens pull requests while you review the diffs. It requires a paid Claude plan or API credits — there is no free tier.

This guide is the overview: what the tool actually is, the five places it runs, what it costs, the core workflow, the extension ecosystem, and the errors you'll hit first. We build and maintain this site with Claude Code daily, so everything below is written from use, not from the marketing page.

What is Claude Code, and how is it different from chat AI?

Chat AI answers questions; Claude Code does work. Ask a chat assistant about a bug and you paste code in, read a suggestion, and apply it yourself. Claude Code inverts that loop: it runs inside your project, finds the relevant files on its own, makes the edits, runs your tests to check itself, and hands you a diff to approve or reject.

Anthropic calls this agentic coding, and after more than a year of daily use we think the label is earned. Three differences from chat AI matter in practice:

1. It has hands. Claude Code reads files, executes shell commands, searches your codebase, runs builds and test suites, and drives git. Chat models describe work; this one performs it — with your approval required at each consequential step, a gate you can relax by turning on automode once you trust a task.
2. It carries context. Recent Claude models accept up to 1 million tokens of context, and the agent gathers what it needs by itself. No copy-pasting files into a chat box, no explaining your folder structure.
3. It iterates. When a test fails or the build breaks, Claude Code reads the error output and tries again — the same feedback loop a human developer runs, just faster.

One boundary worth drawing early: Claude Code is built for code and repositories. If your day is documents, spreadsheets, and slide decks rather than pull requests, Anthropic's sibling product Claude Cowork brings the same delegate-and-review model to general knowledge work — we cover it in What Is Claude Cowork?

The five environments: terminal, VS Code, JetBrains, desktop, and web

Claude Code launched as a terminal-only tool in 2025. By mid-2026 it runs in five environments, all driving the same agent underneath — you pick by where you already work.

Our advice after using all five: learn the terminal version first. It is the reference implementation — every feature lands there before anywhere else — and the IDE extensions reuse its login and configuration. The web version at claude.ai/code is the one we use for fire-and-forget tasks: it runs each session in an Anthropic-managed cloud sandbox and hands back a pull request when it finishes.

If you're weighing Claude Code against an AI-first editor instead, that's a genuinely different trade-off — an agent that visits your existing tools versus an IDE rebuilt around AI — and we've written the full comparison in Cursor vs Claude Code.

Installing Claude Code and signing in

Setup takes about two minutes. The terminal version needs Node.js 18 or newer, then one command:

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

Open a terminal in a project folder and run claude. On first launch it sends you to your browser to authenticate, and the choice you make there matters:

• Sign in with a Claude account (Pro or Max plan) for predictable monthly pricing.
• Sign in with Anthropic Console to bill per token from API credits instead.

The VS Code and JetBrains extensions install from their respective marketplaces and reuse the CLI's credentials; the web version needs no installation at all.

The first thing worth adding to any project is a CLAUDE.md file at the repository root. The agent reads it at the start of every session, so project conventions, build commands, and constraints written there stop being things you re-explain. We're publishing a separate step-by-step Claude Code installation guide that covers Windows, macOS, and Linux quirks in detail.

Is Claude Code free? What it costs in 2026

Claude Code has no separate price tag — it rides on your Claude plan or your API bill. It also has no free tier: Claude's free plan covers chat only, so the honest answer to "is Claude Code free" is no, with Pro at $20/month as the cheapest entry point.

Two numbers put API billing in perspective. Claude Sonnet 5 costs $2 per million input tokens and $10 per million output tokens at introductory pricing (until August 31, 2026; $3/$15 after), while Claude Opus 4.8 costs $5/$25. A single heavy agentic session can burn millions of tokens, so subscriptions are usually the better deal for individuals — the API wins when usage is spiky, shared across a team, or wired into automation.

How to use Claude Code: plan, delegate, review

The mechanics take an afternoon to learn; the judgment takes longer. Here is the loop we run dozens of times a day:

1. Describe the outcome, not the steps. "Add rate limiting to the login endpoint — 8 attempts per 15 minutes per email" beats a file-by-file instruction list. The agent is better at finding the right files than you are at remembering them.
2. Start non-trivial work in plan mode. Plan mode makes Claude Code propose an approach — files to touch, order of operations, risks — before it edits anything. Approving a plan is far cheaper than unwinding a wrong implementation.
3. Let it work, and watch. The agent narrates its tool calls as it goes: files read, commands run, edits made. You can interrupt and redirect at any point.
4. Review the diff like a pull request. This is the non-negotiable step. Claude Code is good; it is not infallible. Everything it writes should pass the same review bar as a colleague's PR.
5. Commit small and often. Small commits keep any misstep cheap to revert.

That review discipline is the whole game. Teams that treat Claude Code as autocomplete-with-extra-steps see modest gains; teams that delegate whole tasks and review rigorously change how they ship. We're writing a full Claude Code tutorial for beginners that walks this loop end to end on a real feature.

Skills, plugins, MCP, subagents, and hooks

Out of the box, Claude Code is a general-purpose coding agent. Five extension mechanisms specialize it to your team and stack:

The pattern across all five is the same: encode your team's knowledge once so the agent applies it every session, instead of being re-told every morning. In our experience, skills and MCP servers pay off first — skills capture procedures, MCP connects the systems your code actually touches, and an off-the-shelf plugin like Anthropic's official frontend design plugin drops a whole capability in with one command. Each mechanism has real depth behind these one-line summaries, and each will get its own dedicated guide on this site: Claude Code skills, MCP servers, subagents, and hooks.

Which model to use inside Claude Code

Claude Code lets you switch models mid-session with the /model command, so this is a per-task choice, not a commitment.

Our rule: default to Claude Sonnet 5 and escalate only when it measurably fails. Claude Opus 4.8 leads SWE-bench Pro at 69.2% and drifts less across long agentic sessions, but Sonnet delivers roughly 97–99% of its coding capability at well under half the cost. The full benchmark data and a decision framework are in Claude Sonnet vs Opus.

Common Claude Code errors and quick fixes

Most Claude Code failures come down to one of three things: authentication, service health, or usage limits. This table covers the ones we actually hit:

Two habits prevent most of this. When errors are 5xx, check status.anthropic.com before debugging your own setup — it's usually them, not you. And glance at your usage limits before starting a long session, because hitting a cap mid-refactor is the most annoying place to stop. We're assembling a dedicated Claude Code troubleshooting guide with the full error catalogue and fixes.

Claude pricing at a glance

For the full breakdown of every plan, see our how much Claude costs guide.