We describe DecAMon, an algorithm for decentralizing the monitoring of the MAS communicative behavior described via an Agent Interaction Protocol (AIP). If some agents in the MAS are grouped together and monitored by the same monitor, instead of individually, a partial decentralization of the monitoring activity can still be obtained even if the "unique point of choice" (a.k.a. local choice) and "connectedness for sequence" (a.k.a. causality) coherence conditions are not satisfied by the protocol.
Given an AIP specification, DecAMon outputs a set of "Monitoring Safe Partitions" of the agents, namely partitions P which ensure that having one monitor in charge for each group of agents in P allows detection of all and only the protocol violations that a fully centralized monitor would detect.
In order to specify AIPs we use "trace expressions": this formalism can express event traces that are not context-free and can model both synchronous and asynchronous communication just by changing the underlying notion of event
