Random Steam Key

Steam support

you will need to figure out the game to create a giveaway for it, otherwise you can drop it in the appropriate thread, try and redeem it and if you already own it find out that way, submit it to steamdb(carries small risk of losing it(unlikely), takes time but it will tell you exactly what the key is for.

If Steam says you already own the game you can check it in browser.

F12 --> Network tab --> try to activate the key --> new ajaxregisterkey line appears --> open purchase_receipt_info --> open line_items --> the name is near: line_item_description