Drop a survey or model file here. The tool works out what format it is, then reports the coordinate system it declares — or, when it declares none, what the coordinates themselves suggest. For IFC it also reports where the georeferencing offset is hidden, since local models rarely name their system.
Nothing leaves this page. Files are read in the browser; there are no network calls and no libraries to load, so this works on a laptop with no connection. A content security policy in the page blocks outbound requests, so that holds even if the code is later changed.
Several at once is fine. Large files are read in place, not copied.