APK (Android application package) file format

Typical contents and structure

Standard components inside an APK include:

• AndroidManifest.xml — declares application components, permissions and required features.
• classes.dex — compiled bytecode for Android's runtime (originally for Dalvik, now generally executed by ART).
• res/ and resources.arsc — compiled resources such as layouts, strings and other assets (resources, including images and sounds referenced inside the app, see assets and media).
• lib/ — optional native libraries compiled for specific processor architectures (for example ARM families; see ARM).
• META-INF/ — cryptographic signatures and certificate information used to verify the package.

Building, signing and distribution

Developers build APKs using Android build tools provided in the SDK. Before an APK can be installed, it must be digitally signed with a certificate to prove its origin; the Android system rejects unsigned packages. App distribution commonly happens through app stores, which deliver APKs to devices, but developers can also distribute APK files directly for manual installation (sideloading). The packaging and delivery process is part of how app software reaches users on the Android ecosystem.

History, evolution and variants

The APK concept has been part of Android since the platform's early releases. Over time the runtime moved from Dalvik to ART, but the APK remains the device-side container. Google Play has introduced alternative distribution formats (for example, the Android App Bundle) that optimize downloads, yet the device typically receives APKs as the installable units.

Security, compatibility and practical issues

Because APKs are executable packages, they can carry malicious code; users should install packages only from trusted sources. Compatibility depends on declared features and included native libraries: a single app can ship multiple native versions for different CPUs or provide resources for multiple screen sizes. Tools exist to inspect, sign, align and optimize APKs during development and release.

For authoritative references and tooling, consult platform documentation and developer guides linked by the platform vendor. Many developers and analysts treat the APK as the fundamental artifact that represents a built Android application and its runtime components.

Format specification • Dalvik/ART bytecode • App resources • Media resources • Processor architectures • Software distribution • Android platform • ZIP format