We present a formal analysis of the Web Services Atomic Transaction (WS-AT) protocol. WS-AT is a part of the WS-Coordination framework and describes an algorithm for reaching agreement on the outcome of a distributed transaction. The protocol is modelled and verified using the model checker UPPAAL. Our model is based on an already available formalization using the mathematical language TLA+ where the protocol was verified using the model checker TLC. We discuss the key aspects of these two approaches, including the characteristics of the specification languages, the performances of the tools, and the robustness of the specifications with respect to extensions.