This paper presents an approach for building SoftWare-Implemented Fault Injection (SWIFI) tools for real-time systems starting from temporal logic specifications. Temporal logic formulas are provided describing the behavior of the main SWIFI mechanisms, both for the injection of faults and for the observation of the target system. Besides conventional fault injectors (i.e., that flip bits in memory and in system calls? parameters), we have also considered fault injectors based on the notion of saboteur. Concerning the observation mechanisms, we have defined on-line software probes aimed at observing not only the failure modes of the system under test, but also the real-time behavior of both the application and the underlying operating system. The specifications of all such mechanisms are then translated into programs that are executed on-line by a virtual machine. This approach was applied to the development of MAFALDA-RT, a SWIFI tool for real-time systems. A case study exemplifies how the proposed approach allows for the SWIFI mechanisms to be defined and applied.