Codex CLI Guide: Bring AI Power Directly to Your Terminal

8/11/2025

Finding Your Way Around the Codex CLI: A Guide for ChatGPT Users

If you're a developer, you've probably spent a good chunk of time in two main places: your terminal & ChatGPT. The ChatGPT web interface is amazing, right? It's like having a senior developer on call 24/7 to help you brainstorm ideas, write boilerplate code, untangle confusing concepts, & even draft emails. It's become an indispensable part of the modern coding workflow.

But here's the thing. As great as it is, it's still a separate window. You're constantly copying code from your editor, pasting it into the chat, copying the response back, & then tweaking it. It works, but it's not seamless. What if you could bring that same AI power directly into your terminal? What if you could have an AI agent that not only talks to you but can also read your project files, create new ones, edit existing code, & even run commands for you?

That’s where the OpenAI Codex CLI comes in. It’s a lightweight, open-source tool that essentially turns your command line into a super-powered, AI-driven development environment. It’s part of a growing trend some are calling "vibe coding," where you interact with an AI agent conversationally to build things. If you're comfortable with ChatGPT, you're already halfway there. This guide is designed to help you bridge the gap, moving from the familiar chat window to the powerful, in-project experience of the Codex CLI.

So, What Exactly IS the Codex CLI?

At its core, the OpenAI Codex CLI is a command-line tool that lets you use OpenAI's most advanced reasoning models right from your terminal. But it's more than just a chatbot in a different skin. Unlike the general-purpose ChatGPT interface, the Codex CLI is a specialized software engineering agent. It’s designed to work directly on your local machine, within your project directories.

This "local-first" approach is a HUGE deal for a couple of reasons. First, security. Your source code stays on your machine unless you specifically ask the AI to share it. It’s not being sent to a chat history in the cloud. Second, context. The CLI can read the files in your current directory, giving it a deep understanding of your entire project. This means its suggestions & actions are far more relevant & integrated than the code snippets you get from a general chat model. It can see how

moduleA.js

interacts with

moduleB.js

& make changes accordingly.

Codex CLI vs. ChatGPT: Why Should I Bother Switching?

This is the big question. If ChatGPT is working so well for you, why learn a new tool? It comes down to the right tool for the right job.

ChatGPT is your brilliant, all-purpose consultant. It's perfect for:

Brainstorming architectural ideas.
Learning a new language or framework.
Generating standalone code snippets.
Explaining complex algorithms.
Writing documentation or comments.

The Codex CLI is your hands-on, in-the-trenches coding partner. It excels at:

Reading & understanding your entire local codebase.
Refactoring existing functions across multiple files.
Creating new files & writing the code for them from a single prompt.
Running terminal commands to install dependencies, start servers, or run tests.
Automating multi-step tasks that involve both coding & execution.

Think of it this way: You'd ask ChatGPT "How do I build a web server in Python using Flask?". You'd tell the Codex CLI, "Build a web server in this directory using Flask & install all the dependencies." It's the difference between asking for a recipe & having a chef in your kitchen who can actually cook the meal for you.

Getting Your Hands Dirty: Installation & Setup

Alright, let's get this thing installed. The process is pretty straightforward, but there are a few key steps.

Prerequisites: First off, to get the best experience, you'll want a ChatGPT Plus, Pro, or Team account. When you link your account, you get access to OpenAI's latest models (like the recently announced gpt-5) at no extra cost to your plan. Plus users even get a $5 API credit, & Pro users get $50, which is a nice little bonus. Also, the Codex CLI is designed to work within a Git repository, so make sure your project folder is initialized with

git init

Installation - Step-by-Step: You can install the CLI using your favorite package manager, or by downloading the binary directly.

Using npm (Node Package Manager): If you have Node.js installed, this is probably the easiest way.