The focus of mzML has always been universal readability, and thus small file size and fast access speed have not been the primary design drivers. As a result, numerous alternatives to mzML that improve on file size and access speed have been proposed, although none seem to have gained substantial usage, perhaps in part because of their dependencies or complexity. A variant of mzML called imzML has become quite common in the imaging MS community, and it is nearly identical to mzML except that the spectra are stored in a more efficient sidecar file instead of the main file. In order to try to consolidate on one particular proposal, the PSI is considering formally approving the HDF5-based mzMLb format as a PSI standard in addition to mzML. The mzMLb format has exactly the same schema and encodes metadata in the same way, and thus interconversion is easy. Adding mzMLb to existing tools is relatively straightforward if the HDF5 dependency can be managed.