Codex CLI (codex)

Codex CLI is OpenAI's agentic coding CLI.

Install

npm install -g @openai/codex

Authenticate

export OPENAI_API_KEY=sk-...

Codex reads OPENAI_API_KEY from the environment. Add it to your shell profile or a .env file.

Configure in millstone

[millstone]
cli = "codex"

Or target a specific role — for example, using Codex only as the reviewer:

[millstone]
cli          = "claude"
cli_reviewer = "codex"

Notes

• millstone invokes codex exec - --yolo, which runs Codex non-interactively and bypasses approval prompts. The prompt is delivered via stdin to avoid OS argument-size limits on large prompts.
• Session resume uses codex exec resume <session_id>.
• Structured output (reviewer and sanity check roles) uses --output-schema <path> with a JSON schema file written to .millstone/.

Further reading

• Codex CLI repository
• Configuration reference
• MCP server setup