We present OpenQuake-Hazard: the seismic hazard calculator of the OpenQuake engine, the seismic risk platform promoted and developed by the Global Earthquake Model initiative. OpenQuake-Hazard is designed to be an open, transparent, and community driven tool for seismic hazard analysis. The source code is hosted on public repositories that allow for distributed development and it’s implemented following modern software design principles like test driven development and continuous integration. It uses an XML-based data exchange format (called NRML, ‘Natural hazard’ Risk Markup Language) and its design reflects the analysis of seismic hazard models produced for different regions of the world (it’s therefore not tight to the needs of a particular geographical/tectonic region).