File created by LackeyCCG, a tool used to create card decks and play collectible card games (CCGs) online or offline; stores a card pool, which is made up of player cards; used for saving decks for different games as well as for different playing styles.

LackeyCCG has been used to create decks for various games such as Magic: The Gathering, Pokémon TCG, Yu-Gi-Oh!, and many others.

Card deck file used by Magic: The Gathering Online (MTGO), an online card-playing game; stores a collection of cards that make up a playable deck for the game; used for saving groups of cards for different races and types of play.

DEK files can be created using MTG Studio. Since they are saved in an XML format, they can also be viewed with any text editor, although it is not recommended that users alter these files manually.

Deck of flashcards that may include text, sound, and images; used by Memorize-It for creating and administering quizzes that can be used for studying and testing knowledge; available for hundreds of different topics.

File used by Yugioh Virtual Desktop (YVD), a game used for playing Yu-Gi-Oh! card games online; saved in plain text and contains a list of cards in the deck separated by line breaks; used for saving decks for different styles of gameplay.