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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

cli = "codex"
codex_yolo = true  # optional: pass --yolo to codex

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

cli          = "claude"
cli_reviewer = "codex"

You can also opt into --yolo from the CLI when needed:

millstone --cli codex --codex-yolo

Notes

  • millstone invokes codex exec - by default. Add --codex-yolo or set codex_yolo = true to pass Codex --yolo explicitly.
  • 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