Descriptor calculation in QSPRpred is facilitated through the DescriptorSet class which wraps one or more types of descriptors. There are many integrated implementations of the DescriptorSet available including: RDKit descriptors , Mordred , Mold 2 , PaDEL and Tanimoto distance to other molecules. Additionally a range of different types of molecular fingerprints are implemented, such as Morgan and MACCs fingerprints. A trained QSPRpred model can itself also be used as descriptor for stacked modelling. While users can add new implementations of DescriptorSets this may not always be practical, for example when using descriptors from experimental measurements. In this case, the descriptors can be provided as a data frame directly via the built-in DataFrameDescriptorSet. Moreover, a custom implementation of the DescriptorSet interface, also exists for protein descriptors (ProteinDescriptorSet) that are commonly used for PCM modelling (i.e. z-scales , BLOSUM and VHSE ). This is provided via the standalone ProDEC package, which enables calculation of multiple sequence alignment-based descriptors for proteins. The multiple sequence alignment is done with Clustal Omega or MAFFT , but QSPRpred also describes an API to easily integrate other alignment methods.