In a distributed system that includes a debug server and debug clients coupled for data communications through a data communications network, where the debug server includes a debug administrator, a message router, a back-end debugger, and a debuggee, collaborative software debugging includes receiving application-level messages, including a request from a requesting debug client to notify other debug clients of an expansion of a multi-member variable; routing the application-level messages among the debug clients, the debug administrator, and the back-end debugger, including providing distributed control of the back-end debugger to the debug clients and distributing, to the other debug clients, a notification of the expansion of the multi-member variable; and returning to the debug clients in response to the application-level messages routed to the back-end debugger, client-specific debug results.