Claude Code

Introduction

Claude Code is an agentic coding tool that runs in your terminal. It understands your codebase and helps you code faster through natural language commands: it can handle routine tasks, explain complex code, and manage Git workflows. This section gets you up and running with AI-powered coding assistance in a few minutes. When you finish, you will know how to use Claude Code for common development tasks.

Claude Code documentation

Installation, usage, commands, and configuration reference

Claude Code GitHub repository

Source code, release binaries, and contribution guide

Prerequisites

Make sure you have:

An open terminal or command prompt
A code project to work on
An API token that supports the Anthropic Messages protocol (how to create a token)

Make sure your terminal environment supports:

# node.js
node -v

# git
git --version

Configure environment variables:

macOS, Linux, WSL
Windows

# manual setup for temporary use
export ANTHROPIC_BASE_URL=https://api.poixe.com
export ANTHROPIC_API_KEY=$POIXE_API_KEY
export ANTHROPIC_MODEL=claude-3-5-haiku-20241022

# add to shell profile for persistent use (add to ~/.bashrc, ~/.zshrc, etc.)
echo 'export ANTHROPIC_BASE_URL="https://api.poixe.com"' >> ~/.bashrc
echo 'export ANTHROPIC_API_KEY="$POIXE_API_KEY"' >> ~/.bashrc
echo 'export ANTHROPIC_MODEL="claude-3-5-haiku-20241022"' >> ~/.bashrc

setx ANTHROPIC_BASE_URL "https://api.poixe.com"
setx ANTHROPIC_API_KEY "$POIXE_API_KEY"
setx ANTHROPIC_MODEL "claude-3-5-haiku-20241022"

Install Claude Code

To install Claude Code, use one of the following methods:

Native Install (Recommended)
Homebrew
WinGet
NPM installation (Deprecated)

macOS, Linux, WSL:

curl -fsSL https://claude.ai/install.sh | bash

Windows PowerShell:

irm https://claude.ai/install.ps1 | iex

Windows CMD:

curl -fsSL https://claude.ai/install.cmd -o install.cmd && install.cmd && del install.cmd

brew install --cask claude-code

winget install Anthropic.ClaudeCode

# Use this method only if you can’t use the native installer.
# Avoid running it with sudo.
npm install -g @anthropic-ai/claude-code

Verify the installation

After installation, run the following command to verify that it succeeded:

claude --version

Start your first session

Open your terminal in any project directory and start Claude Code:

cd /path/to/your/project
claude

You will see the Claude Code welcome screen with your session information, recent conversations, and the latest updates. Type /help to see available commands, or type /resume to continue a previous conversation.

Ask your first question

Let’s start by getting to know your codebase. Try one of the following commands:

> what does this project do?

Basic commands

Here are the most important commands for everyday use:

Command	What it does	Example
`claude`	Start interactive mode	`claude`
`claude "task"`	Run a one-off task	`claude "fix the build error"`
`claude -p "query"`	Run a one-off query, then exit	`claude -p "explain this function"`
`claude -c`	Continue the most recent conversation in the current directory	`claude -c`
`claude -r`	Resume a previous conversation	`claude -r`
`claude commit`	Create a Git commit	`claude commit`
`/clear`	Clear conversation history	`> /clear`
`/help`	Show available commands	`> /help`
`exit` or Ctrl+C	Exit Claude Code	`> exit`

For the full list of commands, see the CLI reference.

Pro tips for beginners

Be specific with your requests

Instead of: “fix the bug”Try: “fix the login bug where users see a blank screen after entering wrong credentials”

Use step-by-step instructions

Break complex tasks into steps:

> 1. create a new database table for user profiles

> 2. create an API endpoint to get and update user profiles

> 3. build a webpage that allows users to see and edit their information

Let Claude explore first

Before making changes, let Claude understand your code:

> analyze the database schema

> build a dashboard showing products that are most frequently returned by our UK customers

Save time with shortcuts

Press ? to see all available keyboard shortcuts
Use Tab for command completion
Press ↑ to see command history
Type / to see all slash commands

FAQ

Why does it show an offline status?

Claude Code checks network status by connecting to Google. Seeing “offline” does not affect normal use; it only means Google could not be reached.

Why does web Fetch fail?

Claude Code needs to call the Claude service for a safety check before accessing a web page. You need to:

Maintain a stable international internet connection
Use a global proxy if necessary

What should I do about API errors?

If you run into an API error:

Confirm that ANTHROPIC_API_KEY and ANTHROPIC_BASE_URL are set correctly
Check your network connection and make sure you can reach the API endpoint
Read the error message and refer to Error handling to troubleshoot
If needed, contact the team for help

How do I exit Claude Code?

In interactive mode, type exit or press Ctrl+C twice to exit Claude Code.

How do I update Claude Code?

One command does it: claude update

Troubleshooting common errors

How do I fix the `Extra inputs are not permitted` error?

While using Claude Code, you may run into the following error:

The error is an API 400: the server returns context_management: Extra inputs are not permitted. Many users report that version 2.1.20 works, but starting with 2.1.22/2.1.23 it fails immediately (any input triggers a 400). What causes this 400? Essentially, the client sent fields (or beta/experimental fields) that the server does not recognize or allow, which causes schema validation to fail. Newer versions of Claude Code include certain context management / beta-related input fields (or the corresponding headers / schema) in requests. But the “backend” you are connected to (commonly an enterprise gateway/proxy, Bedrock/Vertex/Gateway, some relay services, or even an Anthropic API that has been rewritten by a proxy) does not support these fields yet, so it rejects the request under strict schema validation: Extra inputs are not permitted.

Related GitHub issue discussion: https://github.com/anthropics/claude-code/issues/21612

Solution: The official changelog explicitly documents a related fix: In 2.1.27, it mentions “Fixed context management validation error for gateway users”, and notes that setting CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS=1 avoids the error.

Related changelog entry: https://github.com/anthropics/claude-code/blob/main/CHANGELOG.md#2127

Recommendations:

1. Upgrade to version 2.1.27 or later (if you haven’t already)
1. Set the environment variable CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS=1 to disable experimental beta features

Use cases

Chat

Coding

Introduction

Claude Code documentation

Claude Code GitHub repository

Prerequisites

Install Claude Code

Verify the installation

Start your first session

Ask your first question

Basic commands

Pro tips for beginners

FAQ

Troubleshooting common errors

How do I fix the `Extra inputs are not permitted` error?

​Introduction

Claude Code documentation

Claude Code GitHub repository

​Prerequisites

​Install Claude Code

​Verify the installation

​Start your first session

​Ask your first question

​Basic commands

​Pro tips for beginners

​FAQ

​Troubleshooting common errors

​How do I fix the Extra inputs are not permitted error?

Introduction

Prerequisites

Install Claude Code

Verify the installation

Start your first session

Ask your first question

Basic commands

Pro tips for beginners

FAQ

Troubleshooting common errors

How do I fix the `Extra inputs are not permitted` error?