What is Claude Code
Summary — Key Points of This Lesson
- Claude Code is an AI coding tool for developers. It can be used via two frontends: a CLI (command line) and a desktop app.
- It autonomously executes tasks such as reading and writing code, running tests, file operations, and Git operations as an agent — it is not a simple "code completion" tool.
- It is a separate product from Claude.ai's standard chat and Claude Cowork, designed around the core activity of "writing code" for engineers.
- A major update was released in April 2026, adding practically useful features such as cloud routines, auto mode, and /ultrareview.
- Available on paid plans (Pro, Max, Team, and Enterprise). Check pricing in USD before tax.
目次 (5)
Claude Code's Position
Claude Code is a developer-focused AI tool provided by Anthropic. It channels Claude's powerful language capabilities specifically into coding, allowing you to call it directly from a terminal (CLI) to autonomously read and write files, execute commands, run tests, perform Git operations, and more.
You can ask Claude.ai's chat interface to "write some code," but what makes Claude Code different is that it acts directly on your system as an agent. It actually edits files, runs tests, and fixes errors on its own — progressing through this cycle while allowing human review at key points.
CLI and Desktop App
Claude Code has two frontends.
- CLI (Command Line Interface) — The traditional approach of running the
claudecommand in a terminal. You pass a project directory and direct the agent on tasks. - Desktop App — Underwent a major redesign in April 2026. It functions as an integrated development environment combining multi-session parallel execution in a single window, an integrated terminal, a file editor, a visual diff view, and an app preview. Source
The CLI remains the primary interface, with the desktop app serving as its GUI complement. Both operate as "the same Claude Code" — the differences are purely in the frontend.
What You Can Do
The main operations supported by Claude Code are as follows.
- Code generation and refactoring — Given an instruction, it directly edits the relevant files
- Test execution and debugging — A cycle of running tests and autonomously fixing errors
- Code review — Parallel multi-agent analysis via the
/ultrareviewcommand - Git operations — Committing, creating branches, generating PR descriptions, and more
- Cloud routines — Scheduled and event-triggered execution on the Anthropic cloud, even when your PC is closed
Differences from Claude.ai and Claude Cowork
| Product | Primary Audience | Focus |
|---|---|---|
| Claude.ai (Chat) | General users | Conversation and Q&A |
| Claude Code | Software engineers | Coding and development tasks |
| Claude Cowork | General knowledge workers | Completing business tasks (outcomes) |
Detailed Article
For details on the major April 2026 update, see "Claude Code April 2026 Major Update Summary". Harness design is covered in the next Lesson 4-3.
