A common strategy for LC-MS/MS data analysis is to perform spectral matching of the experimental spectra to a library of annotated ones. In untargeted metabolomics, correct spectral annotation helps to avoid rediscovery of already known metabolites. UmetaFlow offers this feature through the OpenMS algorithm MetaboliteSpectralMatcher. The user is required to provide a spectral library in an MGF, mzML or MSP file format, which could either be a publicly available spectral library (e.g., GNPS or MassBank of North America that aggregate spectra from various public libraries and user contributions to one location) or an in-house one. The experimental spectral file that is used as an input is the clustered MS 2 file (MGF) generated from the GNPS export step, and the final output is a feature matrix with MSI level 2 identifications with the highest matching scores (above 60%).