The work we present here is mainly concerned with interagent communication, MAS communication protocols and, in particular, software tools and environments to define, experiment and evaluate actual protocols in MAS. We present a new MAS tool/environment called ProtocolBuilder, implemented in Java, which enables us to effectively support the development and experimentation of MAS communication protocols based on conversations (i.e. exchange of messages between agents). Categories and Subject Descriptors I.2.11 [Distributed Artificial Intelligence]: Intelligent agents and Multiagent systems. General Terms Design, Experimentation, Languages, Verification. Keywords MAS, development environments, software tools, communication protocols, conversations.