Service Oriented Architectures industry aims to deliver agile service infrastructures. In this context, solutions to specify service compositions (mostly BPEL language) and Quality of Service (QoS) of individual services have emerged. However, architects still lack adapted means to specify and implement QoS in service compositions. Typically, they use ad-hoc technical solutions that significantly reduce flexibility and require cost-effective development. Our approach aims to overcome this shortcoming by introducing both a new language and tool for QoS specification and implementation in service compositions. More specifically, our language is a declarative domain-specific language that allows the architect to specify QoS constraints and mechanisms in Web Service orchestrations. Our tool is responsible for the QoS constraints processing and for QoS mechanisms injection into the orchestration. A key property of our approach is to preserve compatibility with existing languages and standards. In this paper, we present our language and tool, as well as an illustrative scenario dealing with multiple QoS concerns.