How the unscrambler works
The tool downloads the site’s local dictionary once, inside a dedicated browser worker. When you submit letters, it counts how many times each letter appears and returns only dictionary entries that can be constructed without using any letter more often than you supplied it.
For example, LISTEN can produce listen, silent, enlist, inlets, and tinsel. It cannot produce a word requiring two of the same letter unless the original rack also contains two copies.