In Boss Clicker, keys are one of the main ways to progress. You can get keys by going to the Anvil and crafting them, but you need a specific set of resources, with the exception of the golden key, which only costs gold. Keys can be used to get weapons or craft items, such as the key box, and can then later be used to craft other things, like the magical casket. To get far in the game, you need to craft keys in bulk.