(2) The PeptideSpectrumMatch class connects a Peptidoform instance to a spectrum defined by a collection, run, and spectrum identifier -analogous to the keys of HUPO-PSI Universal Spectrum Identifier (USI) -and holds all relevant match information and PSM metadata. The psm_utils.io subpackage contains a separate module for each of the (currently) eight supported PSM file formats (Table ). Every module implements a reader and/or writer class to convert the specific PSM file format to, or from, the unified PSMList object. Importantly, these readers and writers also interconvert the various proprietary peptidoform notations from or to ProForma 2.0, which can otherwise be a cumbersome process to perform ad hoc. Consistency between various readers and writers is achieved by inheriting from an abstract base class, providing a blueprint for future implementations of new PSM file formats. Generic read_file and write_file functions could therefore be implemented, where the file type can be specified or set to be inferred from the filename. Similarly, a high-level convert function was implemented for quick interconversion between PSM file formats. Due to this blueprint and the hierarchical architecture of psm_utils, support for more file types can easily be added in the future without requiring changes to the central API.