A watch expression is an expression that is evaluated in the context of a specific stack frame, thread, debug target, process, or launch. Generally, a watch expression is a snippet of code that is evaluated each time a debug target suspends, or when a user provides a context for an evaluation by selecting a debug target or thread. An expression updates its value when it is provided with a context in which it can perform an evaluation.

Clients are not intended to implement this interface. An implementation is provided by the debug platform. Clients that support watch expressions should contribute and implement a watch expression delegate. Watch expressions can be created via the IExpressionManager.