lsforce is a Python-based single-force seismic inversion framework for massive landslides. The codes can also be applied to other seismic sources that are well-approximated as a single force (e.g., volcanic eruptions, some glacial events). The library can be used to invert long period (tens to hundreds of seconds) seismic waveforms to estimate a time series vector of single forces that represents the equivalent forces exerted on the Earth by the landslide.