PSTEP A01 (Space Weather Forecast System) group members at National Institute of Information and Communications Technology (NICT), Electronic Navigation Research Institute (ENRI), and Chiba University have developed and started the service of shortwave propagation simulator (HF-START). It provides real-time shortwave propagation that reflects real space weather information from ground-based observations and model calculations. The HF-START web system has been successfully developed and is now available at https://hfstart.nict.go.jp/. The web calculation function of this system allows shortwave propagation between any two points in Japan based on real-time GNSS observations and between any two points on the Earth based on model-based space weather information. Real-time estimation is possible. The calculation in the past and up to about 1 day ahead in the future is also possible. In addition to amateur radio, HF-START is expected to benefit efficient frequency operation of aviation communications that relies on shortwave in the polar route.