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Introduction

Claude Code is an AI coding agent that runs in your terminal — reading, editing, and executing code across your entire codebase.

Claude Code is a terminal-based AI agent built on Claude. It has direct access to your filesystem, shell, and tools, so you can describe a task in plain language and Claude handles the implementation end-to-end — no copy-pasting, no context switching.

What Claude Code can do

  • Read and edit files — Claude reads source files, writes new content, and makes targeted edits. It shows diffs before applying changes so you stay in control.

    • Run shell commands — Execute tests, build scripts, git operations, and any shell command — with configurable permission controls to keep you safe.

    • Search your codebase — Find files by glob pattern, search content with regular expressions, and navigate large codebases without reading every file manually.

    • Fetch from the web — Pull documentation, read API specs, or search the web — all without leaving your terminal session.

    • Spawn sub-agents — Break complex tasks into parallel workstreams. Claude can spin up and coordinate multiple agents to work on different parts of a problem simultaneously.

    • Connect MCP servers — Extend Claude's capabilities with Model Context Protocol servers for databases, APIs, internal tools, and more.

Permission system

Every tool use in Claude Code goes through a permission check. You control how much autonomy Claude has.

ModeBehavior
defaultClaude asks before running shell commands and making edits. You approve or deny each action.
acceptEditsFile edits are applied automatically. Shell commands still require approval.
planClaude produces a plan and asks for your sign-off before taking any action. Good for reviewing large changes before they happen.
bypassPermissionsAll actions run without prompts. Intended for automated pipelines in sandboxed environments — not for interactive use.

Warning: bypassPermissions mode disables all confirmation prompts. Only use it in isolated environments (Docker containers, CI sandboxes) where Claude cannot affect systems outside the task.

Set your permission mode with the --permission-mode flag when starting Claude, or change it with /permissions which also lets you manage allow/deny rules for specific tools:

claude --permission-mode acceptEdits

CLAUDE.md memory system

Claude Code reads CLAUDE.md files from your repository at the start of every session. These files let you encode project-specific knowledge — build commands, coding conventions, architecture notes, required environment variables — so Claude doesn't need to re-discover them from scratch every time.

There are three scopes:

  • Project (CLAUDE.md at the repo root) — shared by everyone on the team, checked into source control.
  • Personal (CLAUDE.local.md at the repo root) — your private preferences for this project, gitignored.
  • Subdirectory (CLAUDE.md inside a subdirectory) — loaded automatically when Claude works in that directory. Useful for monorepos with distinct modules.

Run /init inside any Claude Code session to generate a CLAUDE.md for your project automatically. Claude analyzes your codebase and produces a file with the commands and context that matter most.

# Inside a Claude Code session
/init

Tip: Keep CLAUDE.md concise. Every line should pass this test: "Would removing this cause Claude to make mistakes?" If not, cut it.

Authentication

Claude Code authenticates in two ways:

  1. OAuth (recommended) — Sign in with your Anthropic account at claude.ai. Run claude for the first time and follow the browser prompt.
  2. API key — Set the ANTHROPIC_API_KEY environment variable. Useful for CI pipelines and non-interactive sessions.

See Authentication for the full priority order and cloud provider options (AWS Bedrock, GCP Vertex AI).

Ready to get started?

  • Quickstart — Get Claude Code running in under 5 minutes

    • Installation — Detailed installation instructions for all platforms
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Quickstart