Rule 903.5 · Commander
Each Commander deck is subject to the following deck construction rules.
Subrules
Each deck must contain exactly 100 cards, including its commander. In other words, the minimum deck size and the maximum deck size are both 100.
Other than basic lands, each card in a Commander deck must have a different English name. For the purposes of deck construction, cards with interchangeable names have the same English name (see rule 201.3).
A card can be included in a Commander deck only if every color in its color identity is also found in the color identity of the deck’s commander.
Example: Wort, the Raidmother is a legendary creature with mana cost {4}{R/G}{R/G}. Wort’s color identity is red and green. Each card in a Wort Commander deck must be only red, only green, both red and green, or have no color. Each mana symbol in the mana cost or rules text of a card in this deck must be only red, only green, both red and green, or have no color.
A card with a basic land type may be included in a Commander deck only if each color of mana it could produce is included in the commander’s color identity.
Example: Wort, the Raidmother’s color identity is red and green. A Wort Commander deck may include land cards with the basic land types Mountain and/or Forest. It can’t include any land cards with the basic land types Plains, Island, or Swamp.
Commander games do not use sideboards.