Several sources of jitter and drift affect the longitudinal phase space dynamics of SwissFEL. To evaluate how drifts can be identified and corrected through appropriate diagnostics and beam-based feedbacks, the response matrix of possible longitudinal diagnostics on laser and RF stability is modeled. To this intent, photocathode laser intensity, laser arrival time, RF phases and RF amplitudes are individually varied in an ELEGANT model, and the expected response of on-line diagnostics on the simulated bunches is evaluated. By comparing the slope of the response to the expected resolution of the instrumentation, suitable monitors can be selected for a feedback.