Benchtop nuclear magnetic resonance (NMR) spectrometers are versatile analytic instruments with low acquisition and operation cost. However, in the basic version, samples must be manually measured one after the other. We herein describe the open-source autosampler RotoMate that allows the automated operation of such instruments. The hardware is easily assembled from 3D-printed and inexpensive off-the-shelf parts, and is controlled by an Arduino Uno. A software package interlinks the operation of the autosampler with the software of the NMR spectrometer and the software for the processing of the spectra. Experiments for up to 30 samples can be inserted into an interactive sample list. The autosampler automatically inserts and ejects the samples, initiates measurements on the spectrometer according to parameters specified in the sample list, and interacts with a common NMR software in the processing and visualization of the obtained spectroscopic raw data. If an internal standard is present, conversions and yields of chemical reactions are automatically calculated, enabling e.g. the monitoring of reactions. The device was fitted to a Magritek Spinsolve instrument and can interact with a free academic version of ACD NMR software to process the spectra, but can likely be adapted to similar instruments and spectroscopy software packages.