How to use Codex CLI: install, AGENTS.md, MCP and exec

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.

1. Install Codex CLI and sign in

On macOS and Linux, the standalone installer is one line:

curl -fsSL https://chatgpt.com/codex/install.sh | sh

Then start it from a project:

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:

/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:

4. Pick up where you left off

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:

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.<name>] table in ~/.codex/config.toml, or in a trusted project’s .codex/config.toml.

A local server needs the command that starts it:

[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:

[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:

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 through the one remote server above, covering every provider you connect.

Using Codex? See how to give Codex production context with Polylane.