rules for sideboard magic

[Gavin]

what are rules for sideboards in magic

[Arix]

In constructed, the sideboard must be exactly fifteen cards - no more, no less (you can also choose not to have a sideboard at all). The four-card rule applies to the deck and sideboard combined, so you can't have four copies of a card in your deck and two in your sideboard. When you sideboard cards in and out, you must do it on a one-for-one basis - that is, for every card you pput in, you have to take one out.

In limited, the sideboard is all the cards you're not using in your deck. When you sideboard card in and out, they don't need to be one a one-for-one basis - you can add in cards without taking any out, or vice-versa, as long as the deck remains at least 40 cards. You can also request extra basic lands.