Annotation of Mass Spectra R package Spec2Annot version 1.3.4 Provides a comprehensive suite of functions to efficiently annotate mass spectra data. Motivated by the need for rapid and accurate chemical identification in high-resolution mass spectrometry, it integrates built-in chemical databases and high-performance C++ algorithms. Users can perform mass-to-charge (m/Z) and retention time searches, determine elemental compositions of molecules using heuristic rules, including specific isotopes, and annotate MS2 spectra with structural metrics using configurable chemistry rules. Software Depends: R (>= 4.0.0) Imports: data.table, magrittr, Rcpp, stringr LinkingTo: Rcpp Suggests: testthat (>= 3.0.0) Sylvain Dechaumet <sylvain.dechaumet@cea.fr> Comprehensive R Archive Network (CRAN) Sylvain Dechaumet [aut, cre], Etienne Thevenot [ctb], Eric Venot [rev], Annelaure Damont [ctb], Anaïs Legrand [ctb] CeCILL 2026-09-26 application/tgz https://CRAN.R-project.org/package=Spec2Annot doi:10.32614/CRAN.package.Spec2Annot