A hammer and sledgehammer appear in the Adventuring Gear table on page 150 of the Player’s Handbook; however, there aren’t any rules for either of them.
My players have asked about them before. I told them the sledgehammer gives you advantage on Strength checks where you could smash something sort of similar to the crowbar. As for the hammer, I wasn’t sure. It’s technically not a tool or a weapon, although I would allow some improvisation for either.
Has anyone found any rulings for hammers and sledgehammers?