CoastSeg is an interactive browser-based program that aims to broaden the adoption of satellite-derived shoreline (SDS) detection and coastal landcover mapping workflows among coastal scientists and coastal resource management practitioners. SDS is a sub-field of coastal sciences that aims to detect and post-process a time-series of shoreline locations from publicly available satellite imagery. CoastSeg is a python package installed via pip into a conda environment that serves as an API for building custom SDS workflows. CoastSeg also provides full SDS workflow implementations via jupyter notebooks and python scripts that call functions and classes in the core CoastSeg API for specific workflows. Two fully functioning SDS workflows are already provided, and more could be added by collaborators in the SDS software community. All API codes, notebooks, scripts, and documentation are hosted on the CoastSeg GitHub repository.