The identification of pesticide residues is a critical application in environmental and food safety analysis. The most common methods for pesticide residue detection and quantification are performed with liquid chromatography tandem mass spectrometry (LCMS) using instruments with varying architectures and characteristics. Pesticides have diverse structural and elemental compositions and often require laborious instrument-specific user optimization to identify ideal adducts and fragment ions. While pesticide transition libraries can be purchased from instrument vendors, little of this information exists in the public domain. The Open Pesticide Transition Library (oPestTL) is an effort to compile a comprehensive list of pesticide ion targets and fragments to facilitate the rapid development of screening methods for any LCMS hardware configuration. While a work that must inevitably evolve, the oPestTL library release detailed here contains over 4,000 individual transitions spread across seven separate LCMS platforms making it the largest openly available collection of pesticide methods ever assembled. The oPestTL library can be freely downloaded or interrogated through an open web application: https://proteomicsnews.shinyapps.io/oPestTLv104/.