The INSPIRE Directive aims to establish an EU interoperable Spatial Data Infrastructure. With the approaching of implementation deadlines, an increasing number of datasets are made available on the INSPIRE Geoportal in the GML format. Within the INSPIRE Maintenance and Implementation Work Programme (MIWP), an Action was started to evaluate and improve client support for INSPIRE datasets. Many desktop and web, proprietary and open source clients (QGIS 2.18 & 3.4, Esri ArcMap 10.5, Esri ArcGIS Online, OpenLayers 3, Leaflet 1.4, OGR, FME and Hale Studio) were tested in: loading/creating/editing data, handling big files, managing geometry (e.g. mixed type geometry), handling CRS, loading/displaying 3D coordinates, managing special properties (e.g. complex data types or attributes with multiplicity > 1). Tests were run on datasets in both GML and GeoJSON formats, the latter being currently studied as alternative INSPIRE encoding. First results show that desktop clients outperform web clients, with QGIS performing the best. A meeting with software vendors to share results and improve client support will be the next step.