Your First Build

Mosayic doesn’t ship pre-built binaries — your dev client has to be built from source, signed with your credentials, and installed on your phone. The good news: Expo Application Services (EAS) automates almost all of it.

What a “dev build” is

A dev build is a development client of your app. It’s like Expo Go, but it’s your app — built with your bundle ID, your dependencies, and your native config. Once installed, it runs whatever JavaScript bundle you point it at, so day-to-day you’ll edit code on your laptop and the dev build picks up changes over Wi-Fi.

You only need to make a new dev build when you:

• Add a native dependency (e.g. a new Expo module)
• Change something in app.json that affects the native build
• Update Expo SDK

For everyday feature work, the JavaScript hot-reloads — no rebuild needed.

App configuration

Before kicking off the build, the dashboard asks you to confirm:

• App name — what shows under the icon on your phone
• Bundle identifier — com.yourcompany.yourapp for iOS, the same string for Android. Once this is set, it’s locked — changing the bundle ID breaks update channels, push notification certificates, and store listings.
• Version — defaults to 0.0.1

The dashboard writes these into mobile/app.json (and mobile/eas.json for build profiles).

Run the build

iPhone

1. Click Start dev build. The extension runs eas build --profile development --platform ios in your mobile/ folder.

2. EAS asks Apple for your provisioning profile and signing certificates. The first time, it walks you through generating them — you’ll need your Apple Developer credentials.

3. EAS uploads your code to its build farm. The build runs in the cloud (this avoids needing Xcode locally for the build itself, though you do need a Mac if you ever want to do a local archive).

4. Wait 5-15 minutes. The dashboard shows a link to the EAS build page where you can watch progress.

5. When the build finishes, you’ll get a .ipa install link. EAS calls this an internal distribution build — it can be installed on registered devices without going through the App Store.

6. Open the install link on your iPhone. iOS prompts you to install. Then go to Settings → General → VPN & Device Management and trust the developer certificate.

Android

1. Click Start dev build. The extension runs eas build --profile development --platform android in your mobile/ folder.

2. EAS generates a signing keystore for you (the first time only) and stores it in your EAS account. Don’t lose this keystore — you’ll need the same one to push updates to the same app on Play Store later.

3. EAS uploads your code and runs the build in the cloud. Takes 5-15 minutes.

4. When done, you’ll get an .apk download link.

5. On your Android phone, open the link and install. You may need to allow installation from your browser in Settings → Apps → Special access → Install unknown apps.

What’s happening behind the scenes

EAS is doing the heavy lifting. The Mosayic dashboard is mostly just kicking off the right eas build command and showing you progress.

You can also see the build directly at expo.dev under your project — useful if you want logs or to re-download an artifact.

Tip

iPhone build failing because of provisioning profiles? This is the most common first-time issue. EAS can usually self-heal if you let it manage credentials (eas credentials:configure) — say “yes” when it asks to manage credentials for you. If it gets stuck, the EAS docs on credentials cover the manual fix.

EAS build limits

The free EAS plan gives you a limited number of builds per month. You can see your usage at expo.dev/accounts/<you>/settings/billing. For most projects this is plenty during early development. If you start hitting the cap (e.g. you’re rebuilding several times a day), the EAS Production plan is $19/mo and gives you priority queue + more builds.

You can also do local builds if you have Xcode and Android Studio set up:

cd mobile
eas build --profile development --platform ios --local

Local builds count against zero EAS quota. They take longer the first time (downloading toolchains) but are fast after that.

Next

You’ve got a dev build installed on your phone. Next: Preview on Your Phone — start your local dev server and watch your app come alive.