Deviation of an expected error rate for a backend server invoked by an application to process a request is used to characterize the backend server health. Performance data generated in response to monitoring application execution is processed to select backend error rate data. The selected data is processed to predict future values of a time series associated with backend error rates. The predicted error rate values are compared to actual error rate values in the time series to determine a deviation from the predicted value. Deviation information for the time series data of error rates is then reported to a user through an interface in a simplified manner.