Build a Minimal AI CLI with Claude in 80 Lines of Node.js

Overview

This tutorial demonstrates how to build a minimal AI command‑line interface (CLI) that talks to Anthropic's Claude model using the official SDK. The entire application lives in a single index.js file (≈80 lines) and requires only Node.js built‑in modules, the dotenv package for environment variables, and the Anthropic SDK with streaming support.

Key Components

Imports : dotenv (load .env), Node's readline (terminal I/O), and the Anthropic SDK ( new Anthropic()) which reads ANTHROPIC_API_KEY from the environment.

Client Setup : Instantiating new Anthropic() creates a client that throws an error if the API key is missing.

Conversation History : An array of { role, content } objects is maintained in memory and sent with every request, providing the AI’s “memory”.

System Prompt : A dedicated message in the messages array defines Claude’s global behavior (e.g., a concise CLI assistant).

Readline Wrapper : Uses Node’s readline to read user input line‑by‑line without extra dependencies.

ANSI Color Helpers : Simple functions that prepend escape codes such as \x1b[36m (cyan) and \x1b[0m (reset) to style terminal output.

chat() Function : Calls client.messages.stream() so tokens are streamed and displayed in real time; the full response is appended to the history array.

Input Loop : An asynchronous recursive function that prompts the user, invokes chat(), and processes two slash commands: /quit / /exit to terminate and /history to dump the raw JSON context.

Entry Point : Prints a banner and starts the input loop.

Prerequisites

Node.js v18 or newer

An Anthropic API key (set as ANTHROPIC_API_KEY in a .env file)

Project Setup

# 1. Clone the repository and enter the directory
git clone https://github.com/Zen-Open-Source/SimpleCLI.git
cd SimpleCLI

# 2. Install dependencies
npm install

# 3. Copy the example environment file
cp .env.example .env

# 4. Paste your API key into .env
ANTHROPIC_API_KEY=sk-ant-your-key-here

Running the CLI

npm start

When started, the CLI prints a prompt such as:

AI CLI  |  输入 /quit 退出  |  输入 /history 查看上下文
You: _

Any line entered is sent to Claude; the response streams back token‑by‑token.

Built‑in Commands

/quit

or /exit – exit the CLI. /history – print the full conversation history as formatted JSON.

How It Works

Stateless API, Stateful Array : Claude’s API does not retain any memory between calls. The application supplies a history array with every request, which the model treats as context.

Streaming : Using client.messages.stream() emits each generated token immediately, allowing the user to see the answer as it is produced instead of waiting for the complete response.

Single‑File Architecture : All logic resides in index.js, making the codebase easy to read, modify, and extend.

References

SimpleCLI repository: https://github.com/Zen-Open-Source/SimpleCLI

Anthropic API console: https://console.anthropic.com

Node.js official site: https://nodejs.org/