DEX code optimization

Optimizing and obfuscating your code using R8 or alternative tools (such as ProGuard-compatible optimizers or secondary DEX post-processors) reduces your app's DEX size, improves runtime performance, and minimizes its memory footprint.

DEX, or Dalvik Executable, files contain the compiled code used to run your app. This typically includes Java and Kotlin code, as opposed to compiled C++ code or .so files.

Measure R8 code optimization locally

To measure your app bundle's uncompressed DEX size locally using the command line, run:

unzip -l <yourapp>.aab | grep -E '\.dex$' | awk '{sum+=$1} END {print sum}'

If your app optimizes with R8, you can measure your app bundle's optimization, obfuscation, and shrinking using the R8 Configuration Analyzer. For detailed definitions of shrinking, optimization, and obfuscation, see Use R8 Configuration Analyzer. The R8 Configuration Analyzer report is also included in the R8 Analyzer Skill.

To inspect the post-optimization metadata embedded in your app bundle (for AGP version 8.10 or higher), extract the r8.json file:

unzip -p <yourapp>.aab BUNDLE-METADATA/com.android.tools/r8.json

Fix the problem

To address low DEX code optimization scores, review the recommendations based on your build system and optimizer:

Android Gradle Plugin and R8

To improve your R8 DEX code optimization scores, see the guidance at Improve R8 optimization. You can also use the R8 Analyzer skill to get additional guidance on optimizing your app's keep rules.

Non-R8 build systems and DEX post-processors

If your build pipeline uses custom build tools or secondary DEX post-processors, take the following steps to improve your app's optimization:

  • Open your app bundle in Android Studio and view it in the APK Analyzer.
  • Select all of the .dex files.
  • Pay close attention to the files with the largest size as you toggle the "Deobfuscate names" button (note: this requires you to upload a mapping.txt file). If you find some of those files stay large while obfuscated, it's likely they're affected by package-wide keep rules.
  • Look either in your proguard-rules.pro file, configuration.txt, or the equivalent for your optimizer if you're not using R8, and search for keep rules that match the packages that aren't getting obfuscated. For example, if com.foo. is a large package in your dex, look for keep rules of the format -keep com.foo.** or -keep com.foo.bar.**.
  • Keep in mind that library consumer keep rules might not be as straightforward to identify. If you suspect a library consumer rule is impacting optimization, you can validate locally by adding it to a standalone sample app using a recent version of AGP, and inspecting it with R8 Configuration Analyzer.