Sleepy is a Python tool for semi-automatic slow wave detection and labelling of brain activity time series data typically measured with EEG. It has multiple slow wave detection algorithms built in and its user interface helps to quickly eliminate false-positives generated by these automated algorithms. By combining an automated approach with only minimal manual intervention, Sleepy can speed up typical workflows by several orders of magnitudes. Sleepy does this by plotting the detected events and allowing the user to quickly flag them as a false-positive using keyboard shortcuts. Events that have been missed by the automated algorithm can be added by the user using the graphical interface as well.