# How to use Codex CLI: install, AGENTS.md, MCP and exec > How to use Codex CLI: install it, sign in, write an AGENTS.md, set permissions, resume sessions, script it with codex exec and add MCP servers. Part 3 of [Using coding agents: Claude Code, Cursor, Codex and more](https://polylane.com/series/using-coding-agents/) Canonical: https://polylane.com/learn/coding-agents/how-to-use-codex-cli/ To use Codex CLI, install it with OpenAI's installer, run codex in your project and sign in with your ChatGPT account. Run /init to create an AGENTS.md, use /permissions to choose what Codex may do, and codex resume to reopen a chat. For scripts and CI, use codex exec, and add MCP servers with codex mcp add. To use Codex CLI, **install it, run `codex` in your project, sign in with ChatGPT, and run `/init` to give it an AGENTS.md.** Choose what it may do with `/permissions`, reopen work with `codex resume`, and use `codex exec` when a script or CI job runs it instead of you. Codex CLI is OpenAI's coding agent for the terminal. It reads your repository, edits files and runs commands from a session in your shell. The steps below follow [OpenAI's Codex CLI documentation](https://learn.chatgpt.com/docs/codex/cli). ## 1. Install Codex CLI and sign in On macOS and Linux, the standalone installer is one line: ```bash curl -fsSL https://chatgpt.com/codex/install.sh | sh ``` Then start it from a project: ```bash cd ~/code/my-app codex ``` The first run asks you to sign in. Choose **Sign in with ChatGPT** to use your ChatGPT plan. ## 2. Give it an AGENTS.md Codex reads project instructions from an AGENTS.md file. Create one from inside a session: ```text /init ``` `/init` writes an AGENTS.md with instructions for Codex based on your repository. Edit it down to what a new engineer would need: how to build, how to run the tests, the conventions that are easy to get wrong. Commit it, so every session and every teammate starts from the same rules. ## 3. Choose what Codex may do Codex asks before it acts outside what you have allowed. Use the `/permissions` slash command to choose what Codex is allowed to do in the session. Start strict on a repository you care about, and loosen it once you trust how it works there. The other slash commands worth learning first: | Command | What it does | | --- | --- | | `/model` | Choose the model and its reasoning effort | | `/status` | Show the current session configuration | | `/review` | Review your changes and find issues | | `/init` | Create an AGENTS.md | ## 4. Pick up where you left off ```bash codex resume ``` `codex resume` reopens a recent chat from the current repository, with its history, so you don't have to explain the task again. ## 5. Run it from scripts with codex exec `codex exec` runs Codex without the interactive UI, which is how you use it from repeatable workflows and pipelines: ```bash codex exec "update the changelog for the commits since the last tag" ``` Keep scripted tasks narrow, with a clear definition of done, and review what they change before it merges. ## 6. Add MCP servers Codex calls tools outside your repository through the Model Context Protocol. Each server is a `[mcp_servers.]` table in `~/.codex/config.toml`, or in a trusted project's `.codex/config.toml`. A local server needs the `command` that starts it: ```toml [mcp_servers.context7] command = "npx" args = ["-y", "@upstash/context7-mcp"] ``` A remote server needs a `url`. If it takes a bearer token, name the environment variable that holds it with `bearer_token_env_var`: ```toml [mcp_servers.polylane] url = "https://mcp.polylane.com/mcp" ``` You can also add servers from the command line with `codex mcp add`. For a server that uses OAuth, finish the sign-in with: ```bash codex mcp login polylane ``` Production is the context Codex usually lacks: it can read the code that failed, but not the logs, traces and deploys that show how. [Polylane gives Codex that context](/for/codex/) through the one remote server above, covering every provider you connect. Using Codex? See [how to give Codex production context with Polylane](https://polylane.com/for/codex/). ## Common questions **How do I sign in to Codex CLI?** Run codex in a project directory. The first time, it asks you to sign in, and you can choose Sign in with ChatGPT. **Where does Codex read project instructions from?** From AGENTS.md. Run /init inside Codex to create one with instructions for your repository, then edit it and commit it. **How do I run Codex without the interactive UI?** Use codex exec. It is the entry point for repeatable workflows and pipelines, such as a CI job. **Where is Codex's config file?** ~/.codex/config.toml by default. A trusted project can also have its own .codex/config.toml. **How do I connect Codex to an MCP server that uses OAuth?** Add the server with its URL, then run codex mcp login with the server's name to complete the sign-in. ## Sources - [Codex CLI (OpenAI docs)](https://learn.chatgpt.com/docs/codex/cli) - [Model Context Protocol in Codex (OpenAI docs)](https://learn.chatgpt.com/docs/extend/mcp?surface=cli) ## About the author ## More in this series [Using coding agents: Claude Code, Cursor, Codex and more](https://polylane.com/series/using-coding-agents/) 1. [How to use Claude Code: a practical guide](https://polylane.com/learn/coding-agents/how-to-use-claude-code/) 2. [How to add MCP servers to Cursor](https://polylane.com/learn/coding-agents/how-to-add-mcp-servers-to-cursor/) 3. [How to use Codex CLI: install, AGENTS.md, MCP and exec](https://polylane.com/learn/coding-agents/how-to-use-codex-cli/) 4. [How to use OpenCode: install, plan and build, MCP](https://polylane.com/learn/coding-agents/how-to-use-opencode/) 5. [How to add MCP servers to GitHub Copilot in VS Code](https://polylane.com/learn/coding-agents/how-to-add-mcp-servers-to-github-copilot/) 6. [How to use the Pi coding agent](https://polylane.com/learn/coding-agents/how-to-use-the-pi-coding-agent/) Previous: [How to add MCP servers to Cursor](https://polylane.com/learn/coding-agents/how-to-add-mcp-servers-to-cursor/) Next: [How to use OpenCode: install, plan and build, MCP](https://polylane.com/learn/coding-agents/how-to-use-opencode/) Get started with one command: `curl -fsSL https://polylane.com/setup | bash` installs the CLI, connects your coding agents, and creates the account.