Claude Code

AI-powered coding agent in the terminal, built by Anthropic. Runs directly in your shell with full access to your codebase.

Official docs · GitHub

Install

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

Launch & authenticate

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$ claude

On first launch, Claude Code opens a browser to authenticate via your claude.ai account (Pro or Max plan required).

Alternatively, set ANTHROPIC_API_KEY to use your own API key directly:

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$ export ANTHROPIC_API_KEY="sk-ant-..."
$ claude

Keyboard shortcuts

Slash commands

Non-interactive mode

Run a single prompt from the command line (useful for scripts and CI):

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# Print mode — output goes to stdout
$ claude -p "Explain the use of context in Go"

# Pipe input
$ cat error.log | claude -p "What does this error mean?"

# With a specific model
$ claude -p "Summarize this file" --model claude-opus-4-5 @src/main.py

File references

Use @ to include file contents directly in your prompt:

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What does this function do? @src/auth/login.py

Refactor @src/api/routes.ts to use async/await

Supports glob patterns:

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Review all test files @tests/**/*.test.ts

Custom instructions

Claude Code reads instructions from CLAUDE.md in the project root (and any parent directories up to ~). Generate it with /init, or let Claude add entries on the fly with #.

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# Project conventions

- Use black for Python formatting
- Run pytest before every commit
- Prefer explicit error handling over bare except

# Commands

- Build: `make build`
- Test: `make test`
- Lint: `make lint`

Global instructions live at ~/.claude/CLAUDE.md.

Permissions

Claude Code asks before writing files or running commands. You can adjust this per session:

Hooks

Hooks are shell commands that run automatically at key points in the Claude Code lifecycle. Define them in ~/.claude/settings.json (global) or .claude/settings.json (project).

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{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Bash",
        "hooks": [
          {
            "type": "command",
            "command": "echo \"Claude is about to run: $CLAUDE_TOOL_INPUT_COMMAND\""
          }
        ]
      }
    ],
    "PostToolUse": [
      {
        "matcher": "Write|Edit",
        "hooks": [
          {
            "type": "command",
            "command": "prettier --write $CLAUDE_TOOL_INPUT_FILE_PATH 2>/dev/null || true"
          }
        ]
      }
    ]
  }
}

Hook events

Hook matchers

The matcher field is a regex matched against the tool name:

MCP servers

Claude Code supports Model Context Protocol servers for extending available tools.

Configure in ~/.claude/settings.json or .claude/settings.json:

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{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/projects"]
    },
    "github": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-github"],
      "env": {
        "GITHUB_PERSONAL_ACCESS_TOKEN": "<token>"
      }
    }
  }
}

Configuration

Settings are stored in ~/.claude/settings.json (global) or .claude/settings.json (project-level):

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{
  "model": "claude-sonnet-4-5",
  "theme": "dark",
  "verbose": false,
  "cleanupPeriodDays": 30
}

Key settings

Workflow: explore → plan → implement

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# 1. Read the codebase without writing anything
Read the authentication module and tell me how sessions are managed.
Don't make any changes yet.

# 2. Plan
How would you add OAuth2 with Google? What files would need to change?

# 3. Implement
Go ahead and implement the plan.

# 4. Verify
Run the tests and fix any failures.

# 5. Commit
Commit these changes with a descriptive message.

Multi-agent with git worktrees

Run multiple independent Claude Code sessions in parallel using git worktrees:

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# Create worktrees for parallel tasks
$ git worktree add ../feature-auth -b feature/auth
$ git worktree add ../feature-api -b feature/api

# Launch agents in each
$ cd ../feature-auth && claude
$ cd ../feature-api && claude    # in another terminal

Update

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$ npm update -g @anthropic-ai/claude-code