Abstract: A tool (KD) for debugging an operating system, which among other elements includes at least one processor (P), a memory (M) for use by the processor, and a memory management unit (MMU). The tool is stored in a zone of the memory (M) where the virtual addressing mode is equal to the physical addressing mode. The tool is operable to perform by a predetermined method, and the tool executes each operation in the physical addressing mode, independently of the management unit (MMU). For controlling the phases of initialization of the machine, the tool supports at least two exception vectors (BP, DSI), and among other elements includes its own stack (S), a decoder (DEC) which uses an algorithm that is operational regardless of the context of the process analyzed and regardless of the storage means (CMM) of the decoded context.