# Codex

> ChatGPT's agent for code: it works in a folder or repository, makes changes, runs tests, and shows every change as a diff for you to review.

**Category:** ChatGPT

**Codex is the software specialist next to Work.** You give it a goal, like fixing a bug or adding a feature, and it reads the real files, edits them, runs commands and tests, and reports back. Every change shows as a [diff](/glossary#diff) you review before you keep it.

You use it in the **Codex view of the desktop app**, in a terminal with the **Codex CLI**, in your code editor, or in **Codex Cloud**, where tasks keep running while your laptop sleeps. A [permission mode](/glossary#sandbox) decides how far it may go alone, and an [AGENTS.md](/glossary#agents-md) file gives it your project's rules.

## At work

Every Monday you clean the same export by hand? Ask Codex for a small script that does it, run it on last week's file, and compare the result.

## Often confused with

Work. Work delivers documents, decks, and Sites; Codex delivers code that runs, with tests, diffs, and Git.

## Related terms

- AGENTS.md
- Diff
- Sandbox

## See it in a lesson

[Codex](/en/learn/chatgpt/advanced/codex)

## Further reading

- [Codex quickstart (ChatGPT Learn)](https://learn.chatgpt.com/codex/quickstart): Your first task in the desktop app.
- [Codex CLI (ChatGPT Learn)](https://learn.chatgpt.com/codex/cli): Installing and using Codex in a terminal.
- [ChatGPT Work and Codex](https://help.openai.com/en/articles/20001275-chatgpt-work-and-codex): How Codex sits next to Work, and usage.

---

Last updated: 14/10/2026  
Source: Rollo Academy glossary