ProGuard

ProGuard is a Java bytecode optimizer, shrinker, obfuscator, and preverifier. It analyzes Java class files to produce optimized, smaller outputs while attempting to preserve behavior. The tool is commonly used in Java and Android projects to reduce application size, improve startup performance, and deter reverse engineering through obfuscation of class and member names.

ProGuard operates through a sequence of passes: shrinking removes unused classes, methods, and fields; optimization applies bytecode transformations that can improve performance; obfuscation renames symbols according to configurable rules; and preverifier simplifies verification by adjusting bytecode. This behavior is controlled by a ProGuard configuration file that specifies input and output jars (-injars, -outjars), library jars (-libraryjars), and a set of rules. Key directives include -keep to preserve classes, methods, or fields (important for entry points and reflection), -dontwarn, and -dontnote to suppress messages.

ProGuard can be run as a standalone tool or integrated into build systems such as Gradle, Maven, or Ant. It supports Java bytecode and is commonly used with Android projects; in recent years Google’s R8 has largely superseded ProGuard in new Android builds, but ProGuard remains compatible and is still used in many existing pipelines.

ProGuard originated as an open-source project and has been maintained by various contributors; in contemporary tooling it is associated with Guardsquare, the company behind related products such as DexGuard. See also: R8, DexGuard.