Deck registration

Players are required to register their decks and sideboards in sanctioned Magic: The Gathering tournament .

From the Tournament Rules (May 13, 2024—Outlaws of Thunder Junction)

• 2.7 Deck Registration
  
  Players are required to register their decks and sideboards (if applicable) in Competitive and Professional Rules Enforcement Level tournaments. The Head Judge may require registration in Regular Rules Enforcement Level tournaments.
  
  Registered decklists record the original composition of each deck and sideboard (if applicable). Once your decklist has been accepted by a Tournament Official it may not be altered. If electronic decklists are used, decklists cannot be altered after the date and time that decklists are required to be submitted.
  
  In Constructed tournaments, decklists must be submitted to a tournament official prior to the start of the tournament.
  
  In Limited tournaments, decklists must be submitted prior to the start of the first round in which that player participates.
  
  Players have the right to request to see their decklist between matches. Such a request will be honored if logistically possible.
  
  Generally, decklists are not public information and are not shared with other players during a tournament. At Professional Rules Enforcement Level tournaments (World Championship, Pro Tour, Regional Championships), opponents’ decklists will be provided to players.
  
  Additional information regarding digital decklists can be found in section 2.12 – Electronic Devices.