Steam – How to list up all Steam Workshop games?

Short of trying out every key one by one to tell what game it's linked to, no, there's no easy way to identify which key belongs to which game.

Thus, the easiest, simplest way, is to try adding the key to your Steam account.

If you do indeed own the game, Steam will not allow you to redeem game, telling you that you already own the game (including the name of it), and that the key will not be redeemed.

However, there is one caveat. Because you don't know which keys correspond to which games, if you have a key for a game you'd not like to add to your inventory (because you're a trader, for example), if you don't have the game in your library, it'll get added in right away.

Here is a possible workaround, according to a reddit thread :

Change your download region (Settings >> Downloads >> Download Region), restart Steam. The downloads should start.