At this moment, adding an API key is optional, but this may change in the future.
Why should I add an API Key?
It's safe - we can protect your skins. If your Steam account gets compromised, when you initiate a deposit, the scammers will try to cancel it and send a new trade of their own. We can detect that and notify you.
It's secure - by having your API Key, we can make sure you're not sending the wrong items to your trade partner by mistake.
It's better - API Key listings have special benefits in the shop. They have a special badge that make them stand out, they will display Float Value information as well as an "Inspect" link and a special item color. This increases the chances of finding a buyer for your item.
It's fast - no more locked listings. Trades will be completed as soon as the buyer will receive your item.
Is this safe?
Yes it is.
We will not share the API Key with anyone and we will keep it safe.
All it allows us to do is view or cancel the trades you are making. We can't send trades on your behalf and we don't have access to your account whatsoever.