Although you can only have 30 cards in a deck in Hearthstone, sometimes you need to compare and contrast. It was difficult to do this with a 30 card limit, but with the 23.4 patch, players can have more than 30 cards in their deckmaker.
What is the overcap feature in Hearthstone?
You can add more than 30 cards to your decks when you go to My Collection. Just keep adding cards until the deck exceeds 30 cards. This is an overcap feature designed to give you more freedom in organizing your cards. If you get out of that specific deck and into another deck, the extra cards will still stay in the deck.
Essentially, the overcap feature allows you to view multiple cards in your deck simultaneously without having to immediately locate the one you want to remove.
Can I play Hearthstone with an overcapped deck?
You cannot play Hearthstone with an overcapped deck. The game will only allow you to play with the legal number, which is 30. When you play Hearthstone and look at the decks you can use, it will appear that the deck has too many cards. To continue using that deck, you can always go to My Collection and lower the cards to 30.
For more on Hearthstone, check out How to earn all rewards for Book of Heroes: Faelin in Hearthstone or How to get Archangel Tyrael for free in Hearthstone here on Pro Game Guides!