What is Codex? How it differs from ChatGPT

Back to the Codex learning hub

What you will be able to do

Understand four different roles

Codex is an agent that can read files, make changes and run commands when the appropriate tools and permissions are available. The model supplies reasoning; the task holds the request and conversation; the environment determines accessible files and tools. A more capable model will not correct a task pointed at the wrong folder. When asking for help, identify the interface, working directory and available tools first.

The distinction from ChatGPT is not simply the application name: current desktop documentation describes Codex work inside the ChatGPT desktop app. Check whether this conversation has a project, can use tools and produces actual file changes or only an answer. A general chat may also have tools; a constrained Codex environment may only support analysis. Judge the capabilities of this particular task rather than its icon or an old screenshot.

Local work uses a folder on the selected computer; cloud work uses a separately configured environment. Identical project names do not automatically synchronize uncommitted files. Mobile remote work also needs a reachable host. See choosing a platform to compare workflows. This lesson uses a local folder in desktop or CLI so that you can readily inspect the result.

First decide: what capabilities does the request need?

Without running a task, classify three scenarios. ① You paste ten lines and ask for an explanation. ② You want packing.txt on your computer changed so that you can open the result after closing the conversation. ③ You want changes in a configured GitHub repository environment for a later diff review. Which requires reading supplied text, local file access or access to a specific remote environment?

The answers are: ① The supplied text is sufficient; access to your whole folder is unnecessary. ② Select the correct local folder and confirm that tools can read and write it; a reply containing revised text is not evidence that the file changed. ③ Configure and select the remote repository and environment; do not assume it has read uncommitted local files. Continue with desktop basics for the second case or cloud tasks for the third. This exercise does not require setting up all three interfaces.

Prepare an independent practice folder

Make sure you can sign in to Codex. If it is not installed, complete desktop setup or CLI setup. This exercise needs only a plain-text editor and terminal, not GitHub, an API key, Node.js or Python. Use your file manager to create codex-orientation in your documents folder. If that name already exists, choose a new one so that old work is preserved.

On Windows, show filename extensions and save from Notepad as All files with UTF-8. On macOS, use plain-text mode rather than RTF. On Linux, use a text editor and preserve filename case. Create the following two complete files in the new folder. Their extensions are .md and .txt; the filename labels outside the examples are not part of their contents.

File one: codex-orientation/README.md. This describes the project for people; a .md extension alone does not turn it into agent instructions.

# Orientation exercise

This folder contains a fictional packing list.
The list has exactly three items.
No website or package installation is required.

File two: codex-orientation/packing.txt. Put each item on its own line; a final newline is fine.

Notebook
Bottle
Umbrella

Step 1: select the folder and inspect it

In desktop, add codex-orientation as a project and create a task. In CLI, open a terminal in this folder and run codex. Opening the entire documents directory may expose unrelated files to the task; narrow the location to this exercise before pasting the prompt below. The English prompt is shared across all translations for comparable results; you may express the same request in your own language.

Inspect this practice folder without changing files.
Report the working directory, list the files, and read README.md and packing.txt.
Explain what this project contains. Cite the filenames supporting your answer.
If a requested file is missing, say so instead of guessing.

Expect two filenames, three items and an explanation that this is not an executable website. Compare the reported path and contents with your file manager. Wording may vary, but the answer must not add unsupported facts. If it only suggests commands for you to run, check whether this interface actually has file tools; instructions for doing work are not evidence that the work ran.

Step 2: request one checkable edit

In packing.txt, replace the line Umbrella with Raincoat.
Preserve the other two lines and leave README.md unchanged.
Do not add files, install tools, or run a website.
After editing, read packing.txt and report exactly what changed.

After allowing the relevant file edit, reopen packing.txt. The three lines should be Notebook, Bottle and Raincoat, with README.md unchanged and no packages or extra files. If a tool asks for access outside this folder, inspect the reason and narrow the task. This exercise does not need unrestricted access to the computer. See permissions and sandboxing for the actual controls.

Step 3: check failure handling and restore

Next ask it to read missing.txt without writing anything and report if the file does not exist. A correct result states that it is missing and leaves the original two files alone. This tests whether the agent guesses when evidence is absent, without deleting anything to manufacture an error. If it invents contents, ask it to inspect the directory again and correct the unsupported statements.

To restore the example, replace Raincoat with Umbrella in your editor, save and read it again. Do not reset an entire project or delete your documents directory. Interrupting a running task stops further work; text already written still needs checking and restoration. Closing a conversation does not undo file edits. Establish this habit before moving on to Git.

Troubleshooting and independent practice

If the contents differ, check for another folder with the same name and unsaved editor changes before repeatedly switching models. If README.md is missing, show its full name and rule out README.md.txt, rich-text formatting and case differences. If you only see an old conversation, verify its computer and project instead of assuming that cloud work can see newly created local files.

Repeat independently: replace Bottle with Cup while preserving order and line count, then restore it. You are finished when you can locate the data, identify the actual changed file, verify all three lines and say which actions were not performed. Continue to your first project and writing a request to apply the same checks to a previewable website.

Interface and product terminology were checked against the desktop documentation and CLI documentation on 2026-09-14. This is an original text-file exercise; available tools and responses depend on your environment. The platform editing instructions are not presented as hands-on Codex tests on all three operating systems.

In the diagram, 01 is the task request, 02 the execution environment and 03 the verifiable file result. Match all three to locate the work.

Back to the Codex learning hub

Read the full description

Task to Environment to Files

• AI tools
• Tutorials
• Codex