These tools look identical — same input, same wordlist, both spit out valid English words. The difference is in the contract. An unscrambler returns every word that can be formed from some or all of your letters. An anagram solver returns only words that use all your letters at the same length.
The math of the difference
Give both tools the letters LISTEN. The unscrambler returns 200+ words: SILENT, TINSEL, ENLIST, plus shorter subsets like LIST, LENS, TIN, SET, IS, and on down to single letters. The anagram solver returns exactly two: SILENT and TINSEL — the only 6-letter English words that use L, I, S, T, E, N exactly once each.
When to reach for each
Unscrambler is the right tool for most letter puzzles: Scrabble, Words With Friends, word-hunt games, and the classic "what can I make with these letters?" question. It's the broader, more forgiving output.
Anagram solver is narrower and pickier. Use it when a puzzle gives you a fixed letter count ("9 letters: rearrange to form a word") or when you're hunting for the exact word someone else had in mind. Its output is small enough to scan by eye.
Behind the scenes
The anagram solver runs in constant time for most inputs because every word in the dictionary is pre-indexed by its sorted letters — "LISTEN" and "SILENT" both hash to the key EILNST, so lookup is one hash table access. The unscrambler is more expensive: it has to generate every subset of your letters and check each against the dictionary. Still under 50ms on a modern browser, but the algorithmic complexity is very different.
Broader results — every word that fits, grouped by length and scored with Scrabble points.