Arm DDT stands out as the premier debugger for servers and high-performance computing (HPC) in research, industry, and educational settings, serving software engineers and scientists who work with C++, C, and Fortran in parallel and threaded environments across both CPUs and GPUs, including those from Intel and Arm. Renowned for its robust capabilities, Arm DDT excels at automatically identifying memory issues and divergent behavior, enabling users to attain exceptional performance across various scales. This versatile tool supports multiple server and HPC architectures, offering seamless cross-platform functionality. Additionally, it provides native parallel debugging for Python applications, ensuring comprehensive support for a range of programming needs. Arm DDT is distinguished by its leading memory debugging features and exceptional support for C++ and Fortran debugging, along with an offline mode that allows for non-interactive debugging sessions. It is also equipped to manage and visualize substantial data sets effectively. Available as a standalone tool or as a component of the Arm Forge debug and profile suite, Arm DDT boasts an intuitive graphical interface that simplifies the process of detecting memory bugs and divergent behaviors across diverse computational scales. This makes it an invaluable resource for engineers and researchers alike, ultimately facilitating the development of high-performance applications.