Codex

Codex is a coding agent built by OpenAI. Think of it as a program that writes code for you based on what you ask it to do.

You can think of Codex as an assistant sitting right next to a developer. If the developer says "add this feature" or "fix this bug," Codex looks at the actual code and either suggests how to fix it or makes the change directly. In the past, developers had to switch back and forth between a code editor and a separate chat window, but with Codex, most of the coding work can happen right inside the chat window.

The ChatGPT desktop app includes not just regular ChatGPT but Codex as well. In other words, Codex isn't a separate standalone program — it's a dedicated feature for developers built into the ChatGPT app.

Articles explain that "the ChatGPT desktop app includes not just regular ChatGPT but also the coding agent Codex." It's important not to mistake Codex for a separate app from ChatGPT — it's a coding-specific feature built into the ChatGPT desktop app.

Open Codex in the ChatGPT desktop app, point it to a code folder you manage, and try asking:

"Find functions in this project that don't have tests yet and write basic tests for them."

Or, if you already know about a bug, paste the error message and ask, "Find the cause of this error and suggest a fix," to get a feel for how it works.