Cross-organisational workflows involve multiple concurrently running workflows across organisations, and are in general more complex and unpredictable than single individual ones. Minor modifications in a collaborating workflow may be propagated to other concurrently running ones, leading to negative impacts on the cross-organisational workflow as a whole, e.g., deadline violation, which can be disastrous for, e.g., healthcare organisations. Worst-case execution time (WCET) is a metric for detecting potential deadline violation for a workflow. In this paper, we present a tool, RPLTOOL, which helps planners model and simulate cross-organisational workflows in a resource-sensitive formal modelling language RPL. The tool is equipped with a static analyser to approximate the WCET of workflows, which can provide decision support to the workflow planners prior to the implementation of the workflow and to help estimate the effect of changes to avoid deadline violation.