Commercial Off-The-Shelf (COTS) electronic components are attractive for space applications. However, fault-tolerant architectures are required to cope with the Single Event Effect sensitivity of these components. CNES has developed a methodology, and the related validation tools, by injecting faults into these fault-tolerant architectures for validation purposes. The methodology is a hybrid one, combining deterministic and random fault injection phases. The main tools used are a boundary scan fault injector, made from an off-the-shelf JTAG tool, and software to analyse and process data obtained from the fault injection tests. This paper highlights the experience feedback relating to both the design and use of these tools, which were implemented to validate fault-tolerant architectures developed by CNES. Although this development has been done in the framework of the space domain, the methodology and tools are applicable for any fault-tolerant systems.