In this paper we presents a tool for the dynamic forecast of performance of linear algebra routine as well as communication between clusters. FAST (Fast Agent's System Timer) is a software package allowing client applications to obtain an accurate forecast of routine needs in terms of completion time, memory space, and number of communication, as well as current system availability. FAST relies on existing low-level software packages, i.e. network and host monitoring tools, and some of our developments in sequential and parallel computational routines modeling. The FAST internals and user interface are presented, as well as experimental results and validation on different applications.