The document describes OPENCoastS, an on-demand coastal circulation forecast service integrated within European resources. OPENCoastS allows users to build forecast systems for selected sections of the North Atlantic coast to run operationally for a defined timeframe. It provides generic tools to build coastal forecast services, addressing limitations of current site-specific and restricted-access efforts. Users can access OPENCoastS by registering at its web platform. The service is currently provided by INCD and being integrated with EGI, available for research users within EOSC-hub. Future access policies include sponsored and market-driven options, with a sponsored or market-driven payment model. Featured use cases summarize forecasts for the Santander estuary and La