The site uses Path of Exiles ladder API which lists the top characters for each of:
- Experience
- Solo Delve Depth (only Path of Exile 1)
To check what level / how much experience / which delve depth is needed to be listed:
- Go to https://www.pathofexile.com/forum/view-forum/leagues-and-race-events
- Pick league
- (If looking for Delve Depth or Solo Delve Depth: Click on the relevant column to sort by it)
- Go to page 750 to look at the end of the list