An expression editor system allows a user to build an expression specifying an action that may occur during execution of a target application. The expression editor system includes an expression editor tool used to create, manage, and store action point definitions that include an action point identifier that specifies an action point located in target application program code. The expression editor system determines from the action point definition a dataset that is in-context at the action point in the application program code, obtains data field selections from the dataset that is in-context at the action point in the application program code, graphically builds an expression, and an outcome that executes depending the expression, links the outcome and the expression to form an action point rule for the action point, and saves the action point rule in the database for execution when the application program code reaches the action point.