Xcode Command Line Tools are tools for software developers that run on the command line, in the Terminal application. Since before Apple's beginnings, this assortment of Unix-based tools have been the foundation of almost all software development. Out of the box, a Mac doesn't contain all of the software and tools needed for programming. Instead, Apple provides a complete development environment named Xcode, available separately for download and installation. Xcode is huge (over 40GB) because it builds software for all Apple operating systems (macOS, iOS, tvOS, and watchOS). Software developers who aren't building software for Apple devices still need the Unix-like tools and utilities installed with the Xcode package. Fortunately, Apple provides a separate and much smaller download, the Xcode Command Line Tools, that installs the most-needed utilities for software development. You can install this smaller package from the Terminal application or as part of installing Homebrew, the popular Mac package manager.