All the grammar debugging tools (the Grammar Analysis, the Sentence Interpreter, the Semantics Stepper, the Sentence Explorer, the Sentence Generator, and the Instantiation Debugger) are accessible through the contextual menu or a key sequence:

These apply to the whole grammar. To debug a specific rule, use the Debug rule menu instead (the Grammar Analysis, Sentence Generator and Instantiation Debugger tools are not available for non-root rules, only for the root rule):

For dynamic grammars, starting one of these tools first opens the context selection dialog.