Convert SB3 to APK

A Scratch project needs Android packaging when it must install from an Android launcher, run without opening Scratch, or be distributed as an app file. The result is an Android application containing the project and a Scratch-compatible runtime, not an editable replacement for the original project.

What SB3 and APK files contain

.sb3 is the project format used by Scratch and compatible editors such as TurboWarp. It is a ZIP-based archive containing project.json, scripts, sprite costumes, sounds, and other assets; Scratch users, educators, and students use it to save and edit projects.

.apk is an Android application package containing an Android manifest, app code, resources, and a digital signature. An APK can be installed directly for testing or private distribution, can appear in the Android app launcher, and can include project assets for offline use. Google Play normally requires an Android App Bundle (.aab) for new applications, not an APK.

Android cannot run an .sb3 file by itself. Packaging must supply a web-based Scratch runtime and wrap it in an Android application.

Package the project with TurboWarp and Android Studio

TurboWarp Packager is the appropriate online tool for turning a Scratch-compatible project into a standalone HTML application. It is not a generic file converter: it packages the project with the runtime needed to execute it. Phosphorus is obsolete for modern Scratch 3 projects, and website-wrapper services such as AppsGeyser do not reliably package the project runtime, assets, permissions, or signing configuration.

1. In Scratch, use File → Save to your computer to retain the original .sb3 file.
2. Open TurboWarp Packager, choose Load from your computer, and select the .sb3 file. Test the preview, including sounds, controls, sprites, and extensions.
3. Select the HTML/web output and download the self-contained HTML package. If the download is named project.html, create a folder named www and rename the file to www/index.html.
4. Install Node.js and Android Studio. In a terminal, create a Capacitor project and add Android support:

mkdir scratch-android && cd scratch-android
npm init -y
npm install @capacitor/core @capacitor/cli @capacitor/android
npx cap init "My Scratch App" "com.example.myscratchapp" --web-dir=www
npx cap add android
npx cap sync android
npx cap open android

Copy the prepared www folder into the project directory before running npx cap sync android. Use a lowercase reverse-domain application ID such as com.example.myscratchapp; it must be unique when publishing.

5. In Android Studio, set the version code, version name, app icon, and any required permissions. Use Build → Generate Signed Bundle / APK; select APK for direct installation or Android App Bundle for Google Play, then create or select a release keystore.
6. Install the signed APK on a physical Android device for testing. Android may require the receiving file manager, browser, or sharing app to be allowed to install unknown apps.

Compatibility and distribution limits

Test on the Android versions and screen sizes that will receive the app. Touch controls, screen orientation, audio autoplay behavior, performance, and hardware keyboard assumptions can differ from the desktop browser.

Camera, microphone, geolocation, clipboard, file selection, and similar Scratch sensing features can require Android manifest permissions and runtime approval. Some browser APIs and custom extensions need native Android changes or will not work inside a WebView.

Scratch cloud variables and Scratch account features are not dependable in a packaged app because they rely on Scratch web-service and session behavior. Use a separate backend or a compatible cloud-variable service if the app requires shared online data.

Keep the original .sb3 file for future editing and archival. An APK or AAB is a deployment package; extracting it does not provide a practical Scratch editing project.