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OpenAI Codex CLI

Codex CLI is OpenAI's terminal-based coding agent. It can read your codebase, suggest changes, and execute commands locally, powered by OpenAI's models.

Installation​

npm install -g @openai/codex

Or via Homebrew:

brew install --cask codex

Starting Codex​

Run it from inside your project directory:

codex

This starts an interactive terminal UI session. Codex can read your repository, make edits, and run commands as you iterate together. You can also pass a prompt directly:

codex "refactor the auth module to use dependency injection"

Authentication​

Codex requires either:

  • A ChatGPT Plus, Pro, Business, or Enterprise subscription (uses your account login via browser OAuth)
  • An OpenAI API key set via OPENAI_API_KEY environment variable

Key features​

Local execution​

Codex runs commands and applies changes on your local machine. It can read files, write code, and run shell commands within a sandboxed environment. You review and approve each action before it executes.

Autonomy modes​

Codex offers three operating modes that control how much it can do without asking:

  • Suggest: read-only, proposes changes but applies nothing (default)
  • Auto Edit: can write files automatically, but asks before running commands
  • Full Auto: reads, writes, and runs commands without confirmation

IDE and desktop integration​

Beyond the CLI, Codex is available as:

  • A desktop app for macOS (with Windows and Linux planned)
  • An extension for VS Code, Cursor, and Windsurf

Multi-model support​

Codex defaults to gpt-5.3-codex but supports other OpenAI models. You can switch models with the --model flag or use the /model slash command during a session:

codex --model gpt-5.1-codex "refactor the auth module"

Tips​

  • Start with Suggest mode until you're comfortable with how Codex interprets your instructions
  • Use specific, scoped prompts for best results (e.g., "add input validation to the signup handler" rather than "improve the code")
  • Codex works best with well-structured projects that have clear file organization

Limitations​

  • Only supports OpenAI models (no Claude, Gemini, or open-source models)
  • Requires a paid subscription or API key
  • Newer than other CLI tools, so the ecosystem and documentation are still maturing