I haven't used the Stardew Predictor but I know mouseypounds Stardew Checkup will indicate missing items.
Yes this a great website.
Regular mines level 100
Stardew Fair buy at prize booth by entrance
Buy one in the sewers from Krobus (get rusty key from Gunther after donating 60 items to museum.)
Complete Museum collection entirely.
Master Angler achievement from Willy.
Secret woods give sweet gem berry (plant a rare seed from traveling cart) to statue of Old Man Canoli
Get married to a single, achieve 12 friendship hearts (can also have Krobus come live with you and reach 12 hearts with him)