Set up Codex in one afternoon

Codex is OpenAI's coding agent, and you don't need to know how to code to get real use out of it. It works on files in a folder you pick: it can clean up a messy spreadsheet, build a web page from a screenshot, or fix a small site, and it shows you every change before you keep it.

Here's the setup I'd do in one afternoon, with a worked example and copyable starters. Codex changed a lot this summer, so if you tried it earlier in the year, it's worth another look. Last checked 27 Sep 2026; use the labels you see in your app.

What changed and what it costs

• It lives in the ChatGPT desktop app now. In July, OpenAI moved Codex into the ChatGPT desktop app for Mac and Windows, next to Chat and Work. There's also a web version, a command-line tool and an extension for code editors, but the desktop app is the one OpenAI recommends to start.
• Free and Go can try it. According to OpenAI's pricing page, Free and Go get Codex in the desktop app with the GPT-6 Luna model, though it's still rolling out, so you may not see it yet.
• Plus ($20 a month) is where it gets useful. You get the stronger GPT-6 Sol model, Codex on the web and your phone, and more usage. Codex and ChatGPT Work share the same allowance, and it resets every five hours with a weekly cap on top.
• New models on September 22. OpenAI released GPT-6 Sol and Luna. OpenAI's docs suggest Sol for everyday work and Luna for simple, repetitive jobs, which uses much less of your allowance.

The five steps, in order

A real one, set up end to end

Here's the whole thing for one person: an Etsy seller who exports her orders every month and spends an evening cleaning up the spreadsheet before she can see what sold.

• The folder is a new folder called "Monthly orders" with a copy of September's orders export inside it. The original stays where it was.
• AGENTS.md says she runs a small Etsy shop, she isn't a coder, she wants plain-English explanations, and Codex should never delete or overwrite the original export.
• The task is to make a clean copy of the spreadsheet (fix the dates, split the product names from the variations, remove test orders) and add a summary of sales by product. Cleaning messy data is one of the uses OpenAI lists for Codex.
• The review shows two new files, the clean spreadsheet and the summary, and the original untouched. She spot-checks five orders against Etsy and finds one refund counted as a sale, so she tells Codex to exclude refunds.
• The skill. Once the numbers match, she asks Codex to save the steps as a "monthly orders cleanup" skill. Next month she drops in the new export and runs it.

By the end, a job that took her an evening takes ten minutes, and she checked the numbers herself before trusting them.

Copyable starters

Paste this into Codex and ask it to save it as AGENTS.md in your project folder. Fill in the brackets first.

# About me and this project
I run [business]. I'm not a developer, so explain what you did in plain English.
This folder is for [project].

# How to work
- Make new files instead of changing my originals, unless I ask.
- Never delete files. Ask me first if something needs to be removed.
- Before a big change, tell me your plan in 3 to 5 steps and wait for my OK.
- If something is missing or unclear, ask. Don't guess numbers or dates.
- When you finish, list every file you created or changed.

Then the first task. This is the spreadsheet cleanup from the example; swap in your own file.

Look at [file name] in this folder. Make a clean copy called
[file name]-clean. Fix date formats, remove blank and duplicate rows,
and split [column] into separate columns if it mixes two things.
Then make a short summary of [totals by product / by month].
Don't change the original file. Tell me anything that looked wrong
in the data so I can check it myself.

If you want to try something visual next, this one builds a simple one-page site you can open in your browser.

Build a one-page website for [business] in this folder using plain
HTML and CSS. Sections: what I offer, who it's for, 3 examples of my
work, and how to contact me at [email]. Use [colors / a screenshot I'll
attach] as the style. It should look good on a phone. Tell me how to
open it in my browser, and don't publish it anywhere.

And the checklist before you call day one done.

[ ] Codex is open on one project folder that only has copies of my files
[ ] Permissions are on "Ask for approval"
[ ] AGENTS.md is saved in the folder and says what to check with me first
[ ] I ran one real task and looked at every file it changed
[ ] I checked the result against the source myself before using it

What goes wrong the first time

It edits the only copy of your file. That's why step two says copies. Your AGENTS.md also tells it to make new files, but a folder of copies is the backup that doesn't depend on it listening.

You run out of usage halfway through. The strongest models use your allowance fastest. For simple, repetitive jobs, switch to Luna, and check how much you've used before starting something big.

You're using Codex for something ChatGPT Work does better. If you just want a document, a deck or a spreadsheet you'll edit yourself, OpenAI's docs point you to Work instead. Codex is best when the job involves a folder of files or building something. And if you want a site hosted online, ChatGPT has a separate Sites feature in beta on paid plans.

You switch on Full access to stop the prompts. The approvals are how you learn what it's doing. OpenAI's own docs warn that even the automatic review mode can make mistakes.

If you already use Claude, the same idea applies to Claude Code, and my Claude setup guide covers the folder, instructions and skills steps. Not sure which plan you need? Read which AI subscription is worth it this fall.