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Codex CLI

An open-source command-line tool by OpenAI that brings AI-powered, chat-driven development directly to your terminal for coding tasks, file manipulation, and code execution.

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OpenAI Codex CLI: AI-Powered Coding Agent in Your Terminal

Introduction

The OpenAI Codex CLI (github.com/openai/codex) is an open-source command-line tool developed by OpenAI. It's designed to bring powerful AI-driven coding assistance directly into the developer's terminal. This tool aims to provide "chat-driven development," allowing users to interact with OpenAI's latest reasoning models using natural language to read, understand, modify, and execute code within their local project repositories.

It's important to distinguish this Codex CLI tool (released around April 2025) from the original OpenAI Codex model that was announced in 2021 and powered early versions of GitHub Copilot. The original Codex model was deprecated as of March 2023, and its capabilities have been succeeded and integrated into newer, more powerful models like the GPT series. The Codex CLI leverages these newer models to provide its functionality.

The target audience for the Codex CLI is developers who are comfortable working in a terminal environment and want an AI assistant that can directly interact with their local file system, run commands, and iterate on code under version control, all while maintaining local execution for these actions.

Key Features

The OpenAI Codex CLI offers several features designed to enhance developer productivity within the terminal:

  • Chat-Driven Development: Interact with the AI using natural language prompts to perform coding tasks.
  • Natural Language to Code: Translate descriptions of desired functionality into code snippets or entire files.
  • Code Understanding & Explanation: Ask the AI to explain existing code blocks or entire files within your repository.
  • File Manipulation: Grant the AI permission to read, write, and modify files directly within your local project.
  • Code Execution: Allow the AI to run shell commands and scripts, and see the live results (with appropriate approval mechanisms).
  • Dependency Installation: Can assist in identifying and installing missing dependencies for a project.
  • Iterative Development: Work with the AI to refine code, fix bugs, and implement features step-by-step.
  • Version Control Awareness: Designed to work within Git repositories, allowing changes to be easily tracked and committed.
  • Multimodal Inputs: Supports passing not just text prompts but also images (like screenshots or diagrams) to guide the AI in implementing features or understanding issues.
  • Configurable AI Models:
    • Supports various models available through what the project refers to as the "Responses API" (likely OpenAI's Chat Completions API or similar, which streams responses and reasoning metadata).
    • Defaults to efficient models like o4-mini (an OpenAI model optimized for speed and cost-effective reasoning).
    • Can be configured to use more powerful models like gpt-4.1 or other compatible models.
  • Approval Modes for Automation Control:
    • Suggest Mode (Default): AI suggests changes (file edits, commands) and requires user approval before execution.
    • Auto Edit Mode: AI can edit files automatically but will still prompt for approval before running shell commands.
    • Full Auto Mode: AI can read/write files and execute shell commands autonomously after initial instruction (use with caution).
  • Local Execution & Privacy Focus: While it calls OpenAI APIs for model inference, the file operations and command executions happen on the user's local machine, and the tool is designed to keep source code and environment variables off the cloud where possible, reducing the risk of IP leakage.
  • Zero-Setup Installation: Easy to install globally via npm.
  • Open Source: The Codex CLI tool itself is open-source under the Apache-2.0 license, allowing for transparency and community contributions.

Specific Use Cases

The OpenAI Codex CLI is designed for various development tasks performed within the terminal:

  • Rapid Prototyping: Quickly scaffold new projects or features with AI assistance.
  • Automated Code Generation: Generate boilerplate code, utility functions, or even entire application modules from natural language descriptions.
  • Debugging: Describe an issue or paste an error message, and have the AI suggest fixes or explain the problem.
  • Code Refactoring: Instruct the AI to refactor specific parts of your codebase.
  • Scripting & Automation: Generate shell scripts or automate repetitive command-line tasks.
  • Learning & Exploration: Understand unfamiliar codebases or explore new programming concepts by asking the AI questions.
  • File System Operations: Use natural language to instruct the AI to create, move, or modify files and directories within your project.
  • Implementing Features from Visuals: Pass screenshots or diagrams to the AI to help it understand and implement UI components or features.
  • Secure Coding Workflows: For developers who prefer to keep their code and terminal operations local while still leveraging powerful cloud-based AI reasoning.

Usage Guide

Using the OpenAI Codex CLI involves installation via npm, setting your OpenAI API key, and then interacting with it in your project's terminal.

  1. Prerequisites:

    • Node.js: Version 22 or newer (LTS recommended). Verify with node -v.
    • npm (comes with Node.js): Verify with npm -v.
    • Git: Version 2.23+ (optional but recommended for full functionality, like built-in PR helpers). Verify with git --version.
    • OpenAI API Key: You need an active OpenAI API key with sufficient credits.

  2. Installation:

    • Install the Codex CLI globally using npm: 
      npm install -g @openai/codex
    • Verify installation (optional): codex --version (though the primary way to start is just codex).

  3. Configuration (API Key):

    • Set your OpenAI API key as an environment variable. The most common way is: 
      export OPENAI_API_KEY="your-api-key-here"
      (For Windows PowerShell, use $env:OPENAI_API_KEY="your-api-key-here")
    • To make this permanent, add the export line to your shell's profile file (e.g., .bashrc, .zshrc, .profile, or PowerShell profile).

  4. Running Codex CLI:

    • Navigate to your project directory in the terminal. If it's not already a Git repository, it's recommended to initialize one: 
      cd /path/to/your/project
git init # If not already a git repo
    • Start in Interactive Mode: 
      codex
      This will launch an interactive session where you can type prompts.
    • Start with an Initial Prompt: 
      codex "Create a Python Flask app with a single endpoint that returns 'Hello, World!'"
    • Non-Interactive (Quiet) Mode (for scripting): 
      codex -q "Refactor the selected Python function to be more efficient."
# Add --json for JSON output

  5. Interacting with Codex CLI:

    • Provide Prompts: Type your requests in natural language. You can ask it to write code, explain code, modify files, run commands, etc.
    • Multimodal Input: You can often drag and drop image files (screenshots, diagrams) directly into the terminal if your terminal supports it and Codex CLI is in a mode to accept them.
    • Approval Workflow:
      • In Suggest Mode (default), Codex CLI will show you proposed file changes (as diffs) and commands, then ask for your approval (y/n/e for yes/no/edit) before applying them.
      • In Auto Edit Mode (--approval-mode auto-edit or -a auto-edit), it will write to files automatically but still ask for approval before executing shell commands.
      • In Full Auto Mode (--approval-mode full-auto or -a full-auto), it will perform file edits and execute shell commands without explicit approval for each step (use with extreme caution).
    • Specify AI Model: Use the --model or -m flag to specify a different OpenAI model compatible with the "Responses API" (e.g., gpt-4.1, o4-mini is often default). 
      codex -m gpt-4.1 "Explain this Rust codebase to me."

Supported AI Models & "Responses API"

  • The Codex CLI is designed to work with OpenAI models that support a "Responses API." This API seems to refer to OpenAI's streaming Chat Completions API or similar endpoints that provide not just the final output but also reasoning metadata or intermediate steps, which is beneficial for an agentic tool like Codex CLI.
  • Default Model: Often o4-mini (a fast and cost-effective reasoning model from OpenAI).
  • Other Supported Models: Users can specify other models like gpt-4.1, gpt-4o, and other "o-series" models via the --model flag or a configuration file.
  • The availability and naming of specific models depend on OpenAI's current API offerings.

Pricing & Plans

  • Codex CLI Software: The Codex CLI tool itself, available on GitHub, is free and open-source under the Apache-2.0 License.
  • OpenAI API Usage Costs: Using the Codex CLI will incur costs based on your usage of the underlying OpenAI models (e.g., o4-mini, gpt-4.1). You are billed by OpenAI for the tokens processed (input and output) according to OpenAI's API pricing for the specific models used.

Frequently Asked Questions (FAQ)

Q1: What is the OpenAI Codex CLI? A1: The OpenAI Codex CLI is an open-source command-line tool that acts as an AI coding assistant. It allows developers to interact with powerful OpenAI reasoning models directly in their terminal to generate code, explain code, modify files, run commands, and automate development tasks using natural language.

Q2: Is this the same as the original OpenAI Codex model from 2021? A2: No. The original OpenAI Codex model that powered early versions of GitHub Copilot was deprecated as of March 2023. This Codex CLI is a newer, distinct tool that uses OpenAI's latest generation of reasoning models (like o4-mini, gpt-4.1) via their API.

Q3: How do I install the Codex CLI? A3: You need Node.js (v22+ recommended) and npm. Install it globally using npm install -g @openai/codex. You'll also need to set your OPENAI_API_KEY environment variable.

Q4: What AI models does Codex CLI use? A4: It can use any OpenAI model available via what it terms the "Responses API" (likely the Chat Completions API with streaming/reasoning capabilities). The default is often o4-mini, but you can specify others like gpt-4.1 or gpt-4o using the --model flag.

Q5: Does Codex CLI run entirely locally? A5: The CLI tool itself runs locally in your terminal. However, it makes API calls to OpenAI's servers for the AI model inference (reasoning, code generation). File operations and command executions (after your approval, depending on the mode) are performed on your local machine.

Q6: Is the OpenAI Codex CLI free? A6: The Codex CLI software is free and open-source. However, using it requires an OpenAI API key, and you will be billed by OpenAI for the API usage based on the models you use and the number of tokens processed, according to OpenAI's standard API pricing.

Q7: How does it handle security and privacy with my code? A7: The CLI executes actions locally. Code context is sent to OpenAI's API for processing. OpenAI's API usage policies apply (e.g., data sent to the API is not used to train their models by default for paying API customers). The Codex CLI offers different approval modes (suggest, auto-edit, full-auto) to give you control over file modifications and command execution, enhancing safety. It can also run in network-disabled and directory-sandboxed modes for increased security during autonomous operations.

Q8: Can Codex CLI work with images or diagrams? A8: Yes, the Codex CLI supports multimodal inputs, meaning you can pass screenshots or diagrams (e.g., by dragging them into supported terminals) to help the AI understand tasks or implement features based on visual references, leveraging the capabilities of underlying multimodal models like GPT-4o.

Related Blog Articles & Tutorials

Community & Support

Ethical Considerations & Safety

  • Code Ownership: You own the code generated by models via the OpenAI API, subject to their terms. The Codex CLI tool itself is Apache-2.0 licensed.
  • Data Privacy: Prompts and code context are sent to OpenAI's API. OpenAI's API data usage policies apply (typically, data sent via the API is not used for training their models by default for paying customers). The CLI tool's local execution of file operations enhances control.
  • Security: The CLI offers approval modes to prevent unintended execution of commands or file modifications. "Full Auto" mode should be used with caution.
  • Responsible AI: Users are responsible for the code they generate and deploy, including testing for security vulnerabilities, bugs, and ensuring ethical use. OpenAI has usage policies to prevent the generation of harmful content.

Last updated: May 16, 2025

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