In the mzSpecLib format, it is possible to annotate individual peaks, as is already done in spectral libraries from NIST (), SpectraST, and PeptideAtlas. However, there have been several different styles of annotations in the past (even from a single provider). To address this, mzPAF describes a single common peak annotation format standard for peptides that is recommended for all peptide libraries and related applications for which peak annotations are desirable.