Build Your First App with Codex (No Experience Needed) | Code with Beto

I show how anyone, even without coding experience, can build a real mobile app using AI-powered tools like OpenAI Codex. I walk you through the exact workflow I use as a professional developer to get an app running on your phone, both iOS and Android.

You’ll learn how to install the necessary tools, create a new Expo project with the right SDK version, and run your app on a physical device using Expo Go. This is a practical, step-by-step guide to reach your first milestone: having a working app on your phone.

What's inside

How people with no coding experience can build real apps today
Installing Expo Go on iOS and Android, including beta versions
Using Bun to manage dependencies and create projects
Setting up a new Expo project with the correct SDK version
Running the app on your phone with Expo Go and scanning the QR code
Signing in to Expo Go to enable app loading
Refreshing the app in Expo Go after code changes
Installing agent skills for Expo to enhance development

How people with no coding experience can build real apps today

The gap between having an idea and seeing it running on your phone has collapsed thanks to AI tools like OpenAI Codex. People can now build apps like habit trackers, games, or productivity tools without writing a single line of code manually.

What unlocks this is knowing how to use AI-assisted coding tools effectively. I emphasize that the app itself is just a vehicle; the key is mastering the workflow that professional developers use when starting new projects with AI help.

Installing Expo Go on iOS and Android, including beta versions

Expo Go is the app that lets you run your React Native projects on your phone. On iOS, the latest Expo Go SDK 55 version may not be available in the App Store, so you need to install it via Apple's TestFlight beta program.

For Android, SDK 55 is not on the Play Store either. Instead, you download the APK from expo.dev/go and install it manually. This ensures you have the latest SDK version compatible with your project.

Checking the Expo Go client version in settings confirms you are running the correct SDK (55 in this video). Having the right version avoids compatibility issues when running your app.

Using Bun to manage dependencies and create projects

Bun is a fast JavaScript runtime and package manager that simplifies managing dependencies for your app. It acts like an App Store for code, pulling open source building blocks from repositories.

You install Bun once on your computer using a simple command (different for Mac or Windows). After installation, you verify it with . Bun is then ready to create new Expo projects and manage dependencies efficiently.

Setting up a new Expo project with the correct SDK version

Using Bun, you run a command to create a new Expo project with the specific SDK version you want (SDK 55 in this video). The command uses a template that matches the Expo SDK version to ensure compatibility.

You name your project folder (e.g., Habit Tracker Codex) and Bun scaffolds the project. This step avoids wasting AI tokens by not prompting Codex to generate the entire project from scratch.

After creation, you open the project folder in Codex and prepare to start the app.

Running the app on your phone with Expo Go and scanning the QR code

Inside Codex, you open a terminal and run to launch the Expo development server. This generates a QR code.

You scan the QR code with your phone’s camera or Expo Go app. The app opens your project on the device, showing the default screen. This live preview lets you see your app running on a physical device instantly.

Signing in to Expo Go to enable app loading

Expo Go now requires you to sign in with an Expo account to load projects. If you see a prompt, open the profile tab in Expo Go and sign in or create an account.

After signing in, scan the QR code again. This time the app loads successfully on your phone. Signing in is a simple but necessary step to use Expo Go with your projects.

Refreshing the app in Expo Go after code changes

When you make changes to your code, Expo Go may not update automatically. You can manually refresh the app by pressing the settings button inside Expo Go and selecting Reload.

This reloads the JavaScript bundle and shows your latest changes on the device. It’s a quick way to verify updates without restarting the entire app.

Installing agent skills for Expo to enhance development

Agent skills are plugins that improve your development experience with Expo inside Codex. You can install these from the plugins section in Codex by searching for “Expo.”

These skills help automate common tasks and integrate Expo features, making your workflow smoother as you build your app.

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