How to convert an AAB to an APK on Android

What is an AAB file, and why can't Android install it?

An AAB is an Android App Bundle. Google's app bundle documentation describes it as "a publishing format" that "defers APK generation and signing to Google Play". Play turns the bundle into a base APK and configuration APKs for each device. Android's package installer doesn't accept an .aab file, so a phone can't install one directly.

To run an AAB on a device, something has to build APKs from it. That something is bundletool, the tool Google says Android Studio, the Android Gradle plugin and Google Play all use to build bundles and convert them into APKs.

How to convert an AAB to an APK with Manifesto

1. Install Manifesto, the APK editor and file manager for Android, and grant All files access on first launch.
2. In the file manager, find the .aab file and long-press it. Next to the usual file actions, Convert to APK is the only package action offered for a bundle.
3. Tap Convert to APK. No dialog opens: the conversion starts right away as a background task named "Converting <file>", and you can follow it in Tasks.
4. When the task finishes with "Converted APK ready", open the folder that holds the AAB. The output is <name>-converted.apk, next to the original.
5. Tap the new APK and use Install on its info sheet, or keep working with it.

Manifesto copies the bundle into private storage, runs bundletool there, takes universal.apk out of the generated APK set and publishes it beside your file. Intermediate files are deleted when the task ends, and a cancelled task leaves no output behind.

What is a universal APK?

A universal APK is a single APK that holds all of the bundle's code and resources for every device configuration. Bundletool builds it with --mode=universal, and Manifesto calls the same UNIVERSAL build mode in code. Google's bundletool documentation lists two trade-offs:

• Bigger file: universal APKs "are larger than those optimized for a particular device configuration", because they carry every ABI, density and language.
• Fused feature modules only: bundletool includes only feature modules whose manifest sets <dist:fusing dist:include="true"/>. A feature module that isn't fused won't be in the APK.

Is the converted APK signed?

The converted APK is signed, because Android only installs signed APKs. Manifesto passes its built-in debug key to bundletool as the signing configuration. Two things follow from that:

• It won't update a Play install. The debug key is not the developer's key, so Android refuses to install the APK over an existing copy of the app. Uninstall the original first.
• The debug key is public. It is fine for testing, not for anything you distribute. To use your own key, long-press the converted APK, tap Sign, choose My keystore under Signing identity, and Manifesto writes <name>-signed.apk. The steps are in how to sign an APK on Android.

The bundle itself can't be signed in Manifesto. Sign isn't offered for an AAB, because bundles use JAR signing rules rather than APK signature schemes; Google's bundletool page notes you "can't use apksigner to sign your app bundle".

Can I edit the AAB and rebuild it?

An AAB is decode and convert only in Manifesto: there is no path from an edited bundle back to a new .aab. If you want to change the app, convert it first, then use Open as project on the converted APK. From there you can decompile DEX to Smali, edit resources and the manifest, and use Build and sign to produce <name>-modified-signed.apk. The APK projects docs and decompile an APK on Android walk through that.

On the phone or on a PC: what's different?

	Manifesto on Android	bundletool on a PC
Command	Long-press, Convert to APK	bundletool build-apks --mode=universal, then unzip universal.apk from the .apks
Output	<name>-converted.apk	An .apks APK set archive
Signing key	Manifesto debug key; re-sign with Sign afterwards	Your keystore with --ks, or a debug key if you pass none
Device-specific set	Not offered for AAB; universal APK only	--connected-device or --device-spec
Needs	Android 8.0+, arm64 device	Java and the bundletool JAR

Limits to know before you convert

• Android version: the AAB engine refuses to run below Android 8.0, which is also Manifesto's minimum, on arm64 devices only.
• Space: the bundle is copied into private storage before conversion, so you need room for the AAB, the APK set and the output.
• No OBB data: Google states that app bundles "do not support APK expansion (*.obb) files", so there is nothing to carry over. If you have a split set instead of a bundle, see install XAPK, APKS and APKM files on Android.

Only convert and modify apps you own or are allowed to analyze.