[almara]

Interesting.

The word list / dictionary provided by the site only had around 170k lines so it must not be a complete version.

I would guess they have excluded some obscure words. I can't see anywhere in the information which dictionary is used.

[almara]

Actually on a second look the wordlist has 279,498 words. I think it was only partially loaded when I first checked.

That bumps the math to log₂(279,498) ≈ 18.1, so 19 guesses in the worst case and about 18 on average with perfect play