Updated project metadata. We have created a synthetic crosslinked peptide library to benchmark crosslinking mass spectrometry search engines. The unique benefit of the library is knowing which identified crosslinks are true and which are false. The data collected from mass spectrometry measurements of the peptide library were used to assess the most frequently used search algorithms. The datasets included will provide an important resource for the crosslinking community to evaluate and optimise search engines, results from which have far-reaching implications.