This article presents our work toward a rigorous experimental comparison of state-of-the-art solvers for the resolution of the satisfiability of formulae in modal logic K. Our aim is to provide a pragmatic way to verify the answers provided by those solvers. For this purpose, we propose a certificate format and a checker to validate Kripke models for modal logic K. We present some experimental results using efficient solvers modified to incorporate this verification step. We have been able to validate at least one certificate for 67 percent of the satisfi-able problems, which provides a set of benchmark with independently checked solution which can be used to validate new solvers. We discuss the limits of our approach in the last part of this article.