OpenAI Codex CLI

OpenAI Codex CLI is OpenAI's official open-source terminal-based coding agent, designed as a lightweight yet powerful tool for autonomous code generation and execution. It represents OpenAI's direct answer to Anthropic's Claude Code, operating in the terminal with the ability to read files, write code, and execute commands within a carefully sandboxed environment that prevents unintended side effects.

The CLI features three distinct operating modes designed for different trust levels: suggest mode proposes changes for manual approval, auto-edit mode applies file changes automatically while still requiring command approval, and full-auto mode executes everything autonomously within a network-disabled sandbox. The sandboxing approach uses OS-level restrictions on both macOS and Linux to enforce strict boundaries around what the agent can modify.

Codex CLI is powered by OpenAI's codex-mini model optimized for low-latency coding tasks, with support for other OpenAI models including o3 and o4-mini for more complex reasoning. It maintains conversation context across interactions, supports multi-file editing, and integrates with git for version control. The project is fully open-source under Apache 2.0, encouraging community contributions and customization.

As a free tool that only requires an OpenAI API key, Codex CLI benefits from competitive API pricing and the broad ecosystem of OpenAI models. Its lightweight design and principled sandboxed execution model make it particularly suitable for developers who want autonomous coding capabilities with strong safety guarantees built into the architecture.