Jetifier is a command line tool developed by Google for Android application developers. Its purpose is to migrate existing Android projects that depend on support libraries to use the newer AndroidX libraries. The tool automatically updates the dependencies, build configuration files, and source code to ensure compatibility with AndroidX. Jetifier can work on both Java and Kotlin projects, making it a versatile solution for developers working with either language. It is an essential tool for developers planning to migrate their applications to AndroidX, as the support libraries are no longer maintained. The tool uses a mapping file to convert the old support library packages to their corresponding AndroidX packages, ensuring a seamless transition. Jetifier also updates the references to the library in XML resource files and Gradle build scripts, ensuring the project remains functional. It offers various command line options to customize the migration process, allowing developers to exclude specific libraries or packages if needed. Jetifier provides detailed logs, making it easy to identify any potential issues or conflicts during the migration process. Overall, Jetifier simplifies the process of migrating Android projects to AndroidX, saving developers time and effort.