AbstractSummaryGenerate Indexes for Libraries (GIL) is a software tool for generating primers to be used in the production of multiplexed sequencing libraries. GIL can be customized in numerous ways to meet user specifications, including length, sequencing modality, color balancing, and compatibility with existing primers, and produces ordering and demultiplexing-ready outputs.Availability and implementationGIL is written in Python and is freely available on GitHub under the MIT license:https://github.com/de-Boer-Lab/GILand can be accessed as a web-application implemented in Streamlit athttps://dbl-gil.streamlitapp.com.