The WIGOS Data Quality Monitoring System (WDQMS) web tool is the result of efforts by the ICG-WIGOS Task Team on WDQMS and of ECMWF (Prates and Richardson 2016), which further developed the web tool and hosts it with the support of MeteoSwiss and the WMO Secretariat (WMO, 2019). The operational version of the WDQMS web tool provides NWP-based monitoring of land-based surface and upper-air (radiosonde) observations. The monitoring categories, availability and quality, are based on near-real-time monitoring information provided by four participating global numerical weather prediction (NWP) centres: the German Weather Service (DWD), the European Centre for Medium-Range Weather Forecasts (ECMWF), the Japan Meteorological Agency (JMA), and the US National Centers for Environmental Prediction (NCEP). The system aggregates NWP monitoring information by station, time interval, observed variable and NWP Centre and generates availability and quality performance reports that are displayed as maps or time series. This User Guide is organized according to the entries and options available on the control panel of the WDQMS web tool to facilitate the users’ search of a particular option. Information on the NWP-based monitoring options as well as on monitoring categories are described in sections 2 and 3, respectively. Details of the temporal aggregation are given in section 4, and information about the participating NWP Centres in section 5. Finally, a summary of the products (maps and time series) available for the two main observation type categories covered by the tool is presented in section 6, and references can be found in section 7.