An In Silico spectral DataBase (ISDB) of natural products calculated from structures aggregated in the frame of the LOTUS Initiative (https://doi.org/10.7554/eLife.70780). Fragmented using cfm-predict 4 (https://doi.org/10.1021/acs.analchem.1c01465) . In silico spectral database preparation and use for dereplication initially described in Integration of Molecular Networking and In-Silico MS/MS Fragmentation for Natural Products Dereplication https://doi.org/10.1021/ACS.ANALCHEM.5B04804 See https://github.com/mandelbrot-project/spectral_lib_builder for associated building scripts. See https://github.com/mandelbrot-project/spectral_lib_matcher for associated matching scripts. The pickle formated ISDBs are build for quicker loading via matchms.