SPOT (SPOT produces our traces), is a C++ library offering model checking bricks that can be combined and interfaced with third party tools to build a model checker. It relies on transition-based generalized Bu/spl uml/chi automata (TGBA) and does not need to degeneralize these automata to check their emptiness. We motivate the choice of TGBA by illustrating a very simple (yet efficient) translation of LTL (linear temporal logic) into TGBA. We then show how it supports on-the-fly computations, and how it can be extended or integrated in other tools.