In a network consisting of several thousands computers, the occurrence of faults is unavoidable. Being able to test the behavior of a distributed program in an environment where we can control the faults (such as the crash of a process) is an important feature that matters in the deployment of reliable programs. In this paper, we present FAIL (for FAult Injection Language), a language that permits to elaborate complex fault scenarios in a simple way, while relieving the user from writing low level code. Besides, it is possible to construct probabilistic scenarios (for average quantitative tests) or deterministic and reproducible scenarios (for studying the application's behavior in particular cases). We also present FCI, the FAIL cluster implementation, that consists of a compiler, a runtime library and a middleware platform for software fault injection in distributed applications. FCI is able to interface with numerous programming languages without requiring the modification of their source code, and the preliminary tests that we conducted show that its effective impact at runtime is low.