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Create your first app

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In this chapter, direct your AI agent to create a new Expo app and see it running on your phone.

For the complete documentation index, see llms.txt. Use this file to discover all available pages.

In this chapter, your agent creates a new Expo app, you get it running on your phone, and you make your first change. This is the loop you'll repeat for the rest of the tutorial.

1

Start your agent in a new folder

Your agent works inside one folder at a time, so create a dedicated folder for this project and start the agent there. In your terminal, run:

Terminal
- mkdir StickerSmash

- cd StickerSmash

Then start your agent in that folder: run claude or codex. If you're using Cursor, create a new folder named StickerSmash, open it with File > Open Folder, and open the agent panel.

2

Create the app

Paste the following prompt into your agent:

Prompt
Create a new Expo app in this folder (the current directory) by running npx create-expo-app@latest and choosing the SDK 54 template — I will test the app with Expo Go on my phone, which uses SDK 54. After it is created, run the project's reset-project script so we start from a minimal app, and delete the app-example folder that the script leaves behind. Don't start the development server; I will run that myself.

The agent takes a few minutes to download the template and install its dependencies. When it finishes, it should report that the project is ready, with a minimal app folder containing a couple of files.

3

Run the app on your phone

This is the one command you'll run yourself throughout the tutorial. It starts the development server that streams your app to your phone. Open a new terminal window (leave your agent running in the first one), then run:

Terminal
- cd StickerSmash

- npx expo start

A QR code appears in the terminal. To open the app:

  • Android: open Expo Go and tap Scan QR code.
  • iOS: open the default camera app and point it at the QR code.

You should see a mostly empty screen on your phone. That's your app. Keep this terminal window open and your phone nearby for the rest of the tutorial.

Phone can't connect?

Your phone and computer must be on the same Wi-Fi network. If they are and the app still doesn't load, stop the server with Ctrl + C and restart it in tunnel mode, which works across networks:

Terminal
- npx expo start --tunnel

You can also find your project under the Projects tab in Expo Go when you're signed in to the same Expo account on your phone and in the terminal.

4

Make your first change

Now close the loop: ask the agent for a visible change and watch it land on your phone. Paste the following prompt into your agent:

Prompt
Change the home screen so it shows the text "Home screen" in white, centered on a dark background with the color #25292e.

What you should see: within seconds of the agent finishing, the app on your phone reloads to a dark screen with white "Home screen" text in the middle:

That's the whole workflow — you prompt, the agent builds, your phone shows the result.

When something looks wrong

Sooner or later a result won't match what you asked for. That's normal, and fixing it is part of the workflow:

  • Describe, don't diagnose. Tell the agent exactly what you see and what you expected: "The text is centered but the background is still white." You don't need to guess why.
  • Paste errors verbatim. If your phone shows a red error screen or the terminal prints an error, copy the whole message into the agent. Error messages are written for programmers, and your agent is one.
  • Ask the agent to check its work. A prompt like "Something is broken — review the change you just made, find the problem, and fix it" goes a long way.
  • If the app gets stuck, shake your phone and tap Reload in the menu that appears. If that doesn't help, stop the development server with Ctrl + C and run npx expo start again.

The next chapters end with a short reminder linking back to this section.

Summary

Chapter 2: Create your first app

You created an app, ran it on your phone, and changed it with a single prompt.

In the next chapter, you'll turn this empty screen into the real thing: navigation tabs, the photo viewer, and an image picker.

Next: Build the home screen