maindeck

Maindeck is a term used in collectible card games to describe the main portion of a player’s deck that is drawn from and used during a game. It is distinct from the sideboard, a separate set of additional cards kept aside and used to adjust the deck between games in a match. The maindeck contains the core components of a deck’s strategy—fighters, removal, counters, mana sources, and synergy pieces—while the sideboard holds targeted tools to address specific opponents or metagames.

In formats that use sideboards, the maindeck’s size is fixed by the format (for example, many constructed Magic: The Gathering formats use a 60-card maindeck with a 15-card sideboard, though sizes can vary by format). Between games in a best-of-three match, players may swap cards between the maindeck and sideboard to improve matchups, keeping the total deck size within the required limit. The sideboard serves as a flexible pool of answers, hate cards, and utility options that are not relied upon in every game.

Deck-building considerations center on balancing the maindeck for broad consistency and common matchups, while placing more situational or matchup-specific tools in the sideboard. Cards that are too narrow for general use are often relegated to the sideboard, though some core pieces may appear in both decks if they provide essential synergy. In formats that do not use sideboards, such as many limited formats or Commander, the maindeck simply represents the entire deck used in play.