Currently, few real sensor Web applications are being explored and some of them are yet to come. Meanwhile, developing and deploying prototypes in order to analyze the sensor Web performance supposes a great effort. Consequently, simulation is fundamental to study sensor Webs, and is being the common way to test new applications and protocols in this evolving research field. This fact has brought a recent growing number of simulation tools available to model sensor Webs. In this paper, we provide background on a number of different sensor webs simulation tools and we discuss the advantages and the drawbacks of each. We also propose an evaluation methodology in order to assess the capabilities of each simulation tool. The results of the evaluation process are analyzed and the open research issues are pointed out providing for an opportunity of improvement of future sensor Web simulators.