Set up Codex

Codex is OpenAI's desktop agent app — a more capable cousin of the ChatGPT chat window. It runs on GPT-5.5, OpenAI's current flagship model (released April 23, 2026). The app is free to install; running skills requires a paid ChatGPT subscription on top (see Step 2).

Codex is positioned as a developer tool, but its Skills and Automations features map cleanly onto how this Playbook works — copy a prompt body into a Skill, attach inputs, run it on a schedule. Every skill in this Playbook works in Codex. If you'd rather use a plain chat-only flow, the regular ChatGPT app at chatgpt.com works too — you just won't get saved Skills or scheduled Automations as named features.

Before you start

You'll need:

• A computer running macOS 11+ (Apple Silicon or Intel) or Windows 10+.
• A work email address — don't use a personal account.
• (Optional but recommended) A folder on your computer where Codex will store the files it produces. Codex asks you to pick a "project folder" on first run.

Step 1 — Download and install the app

macOS

1. Go to developers.openai.com/codex/app.
2. Click the macOS download — it picks Apple Silicon or Intel automatically. (Direct links: Apple Silicon · Intel.)
3. Open the .dmg you downloaded. Drag the Codex icon into the Applications folder.
4. Open Applications, double-click Codex.

Windows

The Windows install runs through the Microsoft Store:

1. Open the Codex listing in the Microsoft Store.
2. Click Get (or Install). The Store handles the download and install.
3. After install, search for Codex in the Start menu and open it.

If you prefer the command line: winget install Codex -s msstore

Linux

Linux is waitlist-only as of May 2026. Sign up at openai.com/form/codex-app if you need it.

Step 2 — Pick a subscription and sign in

When the app opens, you have two ways to sign in:

1. Sign in with your ChatGPT account (recommended) — uses your existing ChatGPT subscription tier.
2. Sign in with an OpenAI API key — for developers who pay per-token. This route disables some features like cloud threads, so use option 1 unless you have a specific reason.

ChatGPT pricing as of May 2026:

Plan	Cost	Use it if…
Free	$0	Codex is included for a limited time, but rate limits will stop you mid-skill. Fine to test, not enough to run real work.
Plus	$20/mo	One person running these skills. This is the right starting point for most readers of this Playbook.
Pro	$200/mo	Heavy daily use, plus access to GPT-5.5 Pro (the deeper-reasoning variant).
Business	$25/seat/mo (2+ seats)	A team using Codex with shared workspace, SSO, and admin controls.
Enterprise	Contact sales	Large org, custom data retention, procurement involved.

Use a work email. Your skills, history, and any uploaded data should live on something your company can audit if needed.

If your company uses single sign-on, click Continue with SSO and follow the prompts. SSO is available on Business and Enterprise.

Step 3 — Pick your project folder

The first time you sign in, Codex asks you to choose a project folder — a directory on your computer where it will read and write files for tasks you give it.

For non-developer skills (CSV analysis, scorecard generation, content drafting), pick or create a fresh folder like Documents/Playbook or OneDrive/Marketing AI. You can switch folders later from the top-left folder picker.

Step 4 — Send your first message

After picking a folder, Codex opens to its main thread view. The text box at the bottom is where you type. Try this:

Hello. I just installed Codex. Reply with one sentence so I know the app is working.

Press Enter. Codex responds within a few seconds. The install is verified.

Step 5 — Try attaching a file

Most skills in this Playbook hand Codex a file to read. Practice once now:

1. Find any spreadsheet or PDF on your computer.
2. Drag it into the Codex thread, or click the paperclip / attach icon at the bottom-left of the message box.
3. After it uploads, type: Describe this file's structure in three sentences. Press Enter.

Codex reads PDFs, CSVs, XLSX, DOCX, plain text, code, and images directly.

Step 6 — Create your first Skill (this is where prompts live)

A Skill is a saved prompt — the instruction body that turns Codex into a specific reusable tool ("monthly distributor scorecard," "competitive comparison memo," etc.). Skills are reusable across the Codex app, the Codex CLI, and the Codex IDE Extension.

1. In the left sidebar, click Skills.
2. Click New Skill.
3. Name it after the Playbook skill you're setting up — e.g., Monthly distributor scorecard.
4. Paste the skill's prompt body into the Instructions field.
5. Save.

The Skill now appears in your left sidebar.

Step 7 — Load your first skill from this Playbook

1. Open any skill page in this Playbook (left sidebar → Skills).
2. Find the section called The prompt and click the Copy button.
3. Switch to Codex. Click Skills → New Skill. Paste the prompt body into Instructions. Save.
4. Click the new Skill in the sidebar to start a thread against it. Attach the files the skill's Inputs to attach list names. Type Run the skill. and press Enter.

That's the loop for every skill in this Playbook: copy the prompt → save as a Codex Skill → attach the inputs → run.

(Bonus) Run a skill on a schedule

Codex has a built-in Automations feature for scheduled tasks. If a skill is something you want Codex to run every Monday at 8am (instead of you opening the app and clicking Run), you can wire that up here. See the Scheduled tasks reference page for the full setup.

When something goes wrong

• "I don't see a Skills tab." You're signed in with an API key, or you're on a tier that doesn't include the desktop app's Skills feature. Sign out, sign back in with your ChatGPT account, and check Settings → Subscription.
• "Codex says it can't read my Excel file." Save a copy as CSV (File → Save As → CSV UTF-8 in Excel). Codex handles CSVs more reliably than XLSX with merged cells, pivot tables, or macros.
• "The output mentions a file I didn't attach." GPT-5.5 occasionally fabricates input file names if the prompt expects attachments and none are present. Always confirm every file in the skill's Inputs to attach list is in the thread before saying "Run the skill."
• "The output is too generic." Add a one-line constraint to your message: Use only the attached files. Don't infer from outside knowledge. Most generic-output cases are GPT-5.5 falling back on training data when it doesn't see expected inputs.
• "I'm rate-limited mid-skill." Free tier rate-limits aggressively; Plus has hourly windows. Wait an hour or upgrade. Pro effectively removes this for marketing-skill workloads.
• "My install on Windows says 'Microsoft Store unavailable.'" Some corporate Windows builds disable the Store. Ask IT to enable it for your account, or use the winget command above (which still goes through the Store backend but doesn't open the Store UI).

Where to go next

• AI terminology — what "skill," "thread," "context window," and "agent task" mean in this Playbook.
• Using skills — the four-step pattern every skill in this Playbook follows.
• Scheduled tasks — how to make a skill run automatically with Codex Automations.