Codex CLI
OpenAI's open-source terminal coding agent. A strong, scriptable second opinion that pairs well with a primary agent.
Codex CLI is OpenAI’s open-source, terminal-native coding agent. I do not run it as my primary — I run it as a second opinion, and in that role it earns its place.
What it is good for
It is scriptable and open. Because the source is available and it runs headless cleanly, it slots into automation: a review pass, an adversarial “try to break this” pass, a quick consult. Running a task through a different model and comparing notes catches things a single agent misses.
It is direct. The output is terse and technical, with little hedging — useful when you want a blunt read on a diff.
Where it falls short
As a primary driver it is less smooth than the best agentic tools — the loop ergonomics and multi-file coordination are a step behind. And it depends on API access, so “open-source” does not mean free to run.
Verdict
Worth keeping installed as your second opinion even if it is not your daily driver. Use it.
Changelog
- 2026-05-13 Retested on 0.40 — second-opinion role holds, rating held at 8.
- 2026-04-28 Added to the Stack at 8/10.