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Introduction to Claude Code

Claude Code is Anthropic's agentic coding CLI. It reads files, writes code, runs commands, and iterates on tasks on its own — closer to a development partner than to an autocomplete tool.

Anthropic describes it as "an agentic coding tool that lives in your terminal, understands your codebase, and helps you code faster through natural language commands" (Claude Code docs). It runs on Anthropic's Claude models (Sonnet 4.5 and Opus 4.5) and installs via the @anthropic-ai/claude-code npm package.

Claude Code is not Claude.ai (the consumer web chat) and not the Anthropic API. It uses the same models but wraps them with tool use, file editing, and terminal execution. For background on the wider category, see the agentic AI overview; for a worked example, see building a reminder plugin with Claude Code.

What is Claude Code?

Claude Code is:

  • A CLI tool that runs in your terminal alongside your existing workflow
  • Agentic: it plans multi-step tasks, executes them, and verifies the results
  • Tool-enabled: it reads and writes files, runs shell commands, searches code, and uses git
  • Context-aware through CLAUDE.md files in your project

Key Capabilities

Capability Description
Multi-step Planning Breaks complex requests into executable steps
File Operations Reads, creates, and edits code files
Shell Execution Runs builds, tests, linters, and other commands
State Tracking Maintains context across operations within a session
Subagent Delegation Spawns specialized agents for focused tasks
Verification Uses tests and checks to validate changes

When to Use Claude Code

Claude Code excels at:

  • Exploratory coding – "How does this auth system work?"
  • Refactoring – "Extract this into a reusable module"
  • Debugging – "Why is this test failing?"
  • Documentation – "Generate docs for this API"
  • Multi-file changes – "Add error handling across all endpoints"

Getting Started

  1. Install – Follow the official installation guide
  2. Configure – Create a CLAUDE.md file in your project root
  3. Run – Use claude command in your terminal

The CLAUDE.md File

The CLAUDE.md file is your project's instruction manual for Claude Code. It defines:

  • Workflow patterns (plan → test → implement → verify)
  • State management preferences
  • Tool usage policies
  • Completion criteria

Without one, Claude falls back on defaults; with one, it follows the process you spell out.

→ Learn more: Writing Claude.md