Ladybug is a free and open source environmental plugin for Grasshopper to help designers create an environmentally-conscious architectural design. The initial step in the design process should be the weather data analysis; a thorough understanding of the weather data will, more likely, lead designers to high-performance design decisions. Ladybug imports standard EnergyPlus Weather files (.EPW) in Grasshopper and provides a variety of 2D and 3D designer-friendly interactive graphics to support the decision-making process during the initial stages of design. The tool also provides further support for designers to test their initial design options for implications from radiation and sunlight-hours analyses results. Integration with Grasshopper allows for an almost instantaneous feedback on design modifications, and as it runs within the design environment, the information and analysis is interactive. Check the source code on Github and download the latest stable version from Food4Rhino.