OpenAI Codex CLI Is Open Source

Melvin Vivas · X post · 2026-05-09 · Open on X

Topics: AI Dev Tools & Productivity, AI Agents, Tool Use & MCP · Level: beginner

Summary

Points out that OpenAI's Codex CLI coding agent is open source. That means you can read its code, use it for free and learn how a terminal coding agent is built.

Key points

• Codex CLI is open source.
• You can read the code to learn how a terminal coding agent works.

Resources mentioned

• OpenAI Codex · tool · openai.com · paid
  OpenAI's coding agent. In the diagram it writes code, fixes review findings and drives the build loop. The creator also used it to make this video.
  Also in: An agent bot that installs and drives Codex on its own (Melvin Vivas on X · notes), Asking a Coder bot to install Codex (Melvin Vivas on X · notes), Sign in with ChatGPT: Setting Usage Limits for Each App (Melvin Vivas on X · notes), Codex Cloud Environments Must Be Saved & Published Before Use (Melvin Vivas on X · notes) and 240 more

Try this

• Look through the Codex CLI repo to see how a coding agent is built.