The Libra tool is designed for isobaric labeling datasets, such as iTRAQ and TMT . It reads as input a protXML file as well as the corresponding pepXML and mzML files, deriving abundance measurements based on the reporter ions in each spectrum. Isotopic corrections are applied based on batch-to-batch variation spec sheets provided with labeling kits. While originally published for the 4-channel iTRAQ reagents, Libra has been periodically extended to support the ever-growing multiplexing possibilities and now supports up to 32 reporter ions per spectrum, and is not limited to any specific set of reagent tags.