Earthly is a build automation tool that enhances build efficiency by leveraging a sophisticated caching mechanism, enabling users to automatically cache build components, thereby accelerating the build process. The tool structures build files, known as Earthfiles, to optimize caching by layering commands akin to a multi-layered cake, where each command forms a reusable cache layer. If a command's input changes, it causes a "cache bust," triggering re-execution of that command and subsequent layers. Users can further optimize builds by structuring Earthfiles to separate frequently changed files, thus minimizing unnecessary cache invalidation. Earthly also supports modular build structures, allowing for reuse of cached dependencies across different build targets, which can be beneficial for tasks such as application previews or testing. Additional Earthly features, such as cache mounts and Earthly Cloud, offer further enhancements for build speed, while Earthly Satellites can expedite continuous integration processes.