An in-process debugging experience can be implemented using an infrastructure that supports out-of-process debugging. A program that is to be debugged may be written in a command-line language that receives and processes input through an input loop. The interpreter for the language runs in a first process. A helper program is started in a second process, and attaches to the first process as if it were an out-of-process debugger. A debugging module is loaded into the interpreter, which provides user debugging commands that may utilize the helper program. When the program to be debugged generates a debug event, the event is received by the helper process, which uses a debug primitive to start a new instance of the input loop in the first process. Debugging commands provided by the debugging module can be entered by the user into the new instance of the input loop.