Not a GUI/webapp, but I like to use ncdu snapshots ("exports"). ncdu is an interactive file browser / disk usage analyzer with a terminal UI, which allow for convenient browsing but also, y'know, figuring out what to delete in case of storage cleanups.
creating a snapshot ("exporting"):
ncdu /pathyouwanttoscan -2 --one-file-system --compress -o snapshot_ncdu.json.zstd
(-2 enables progress bar and error messages during the scan)
reading ("importing"):
ncdu -f snapshot_ncdu.json.zstd