CLI agent
OpenAI Codex
OpenAI's coding agent, available as a command-line tool, an IDE extension and a cloud service. You sign in with a ChatGPT account.
Free tier MCP support Open source
Pricing
OpenAI's pricing page says Codex is included with ChatGPT plans, and lists Plus, Pro, Business, Edu and Enterprise with access in the CLI and IDE extension. It also shows a Free plan described as a way to explore Codex on quick coding tasks, but it isn't clear what the Free plan includes, so check before relying on it. You can instead use an OpenAI API key and pay API rates, though that doesn't include cloud features such as GitHub code review. Plans change, so see OpenAI's pricing page for current details.
Pros
- CLI, IDE extension and cloud, so you can pick how you work
- Reads AGENTS.md for project instructions
- Supports MCP servers and Agent Skills (SKILL.md)
- Installs with npm, Homebrew or OpenAI's install script
Cons
- Terminal-first, like Claude Code
- Full access needs a paid ChatGPT plan or API credits
Guides for OpenAI Codex
Guide
A practical workflow for reviewing AI-written code
Intermediate · 8 min read
GuideAGENTS.md explained: one instructions file for many AI coding tools
Intermediate · 8 min read
RecipeGet started with OpenAI Codex CLI: install it and make your first change safely
Beginner · 7 min read
RecipeConnect OpenAI Codex to MCP servers
Beginner · 7 min read