Tools are objects that intercept musical messages and process them before they are passed on to the port. All tools (except the output tool implemented by DirectMusic) are application-defined.
The IDirectMusicTool interface represents a single tool. The methods of this interface are implemented by the application or DLL in order to define the tool's functionality.
Tools are collected in a graph, represented by the IDirectMusicGraph interface, which is implemented by both the segment and the performance object. The interface is used for directing messages from one tool to the next as well as for adding tools to the graph, retrieving pointers to individual tools, and shutting down the graph.