Your habit tracker works in Expo Go. Before it can go on Google Play, it needs a proper name, an icon, and a few screenshots. All of this starts in one file.

That file is app.json, called the app config. Think of it like the label on a bottle of water. The water is your code. The label says the brand name, shows the logo, and has a barcode that is never reused. Your code does not change. Only the label does.

{
  "expo": {
    "name": "Daily Habits",
    "slug": "daily-habits",
    "icon": "./assets/images/icon.png",
    "android": { "package": "com.nusratdev.habits" }
  }
}

• name is the name under the icon on the home screen.
• slug is a short id for your project on expo.dev. People never see it.
• icon is the picture. The Expo docs say 1024x1024 PNG is a good size, and it must be exactly square.
• android.package is the barcode. It is your app's id on Google Play, like com.nusratdev.habits. Small letters, numbers and _, separated by dots. Pick it once, carefully. After you publish, never change it. The Android docs say Play treats a new package as a completely different app.

Android phones cut icons into different shapes: a circle on one phone, a rounded square on another. So Android uses an adaptive icon: a front layer (your logo) on top of a back layer (a colour). In app.json this is android.adaptiveIcon with foregroundImage and backgroundColor. The Android docs say each layer is 108x108 dp, and only the middle 66x66 dp is always safe from cutting. So keep your logo small and in the centre, with empty space around it.

The splash screen is the picture shown for a moment while the app opens. In current Expo SDKs you set it with the expo-splash-screen plugin in app.json: an image, an imageWidth and a backgroundColor. Expo Go shows its own icon here, so the docs say to check your splash screen in a real build, which you make in the next topic.

Screenshots come from your own phone. Open the app, add three real habits, and take screenshots of your best screens. Google Play has rules for them (as of October 2026): JPEG or PNG without transparency, each side between 320 and 3840 pixels, and the long side can't be more than twice the short side.

People often upload phone screenshots straight from a modern phone. Many phones today make screenshots like 1080x2400. That is more than twice as tall as it is wide, so Play refuses it. Crop it to 1080x1920 (9:16), or place it on a 1080x1920 background in Figma or Canva.

When you read an app.json, look for four things: the name people will see, an android.package you are happy to keep forever, icon files that really exist at those paths, and an adaptive icon with a background colour that matches your logo.