What is a DEK file?
A .DEK file is most commonly a Magic: The Gathering Deck File created by Wizards of the Coast. Players use this file to save, build, and share custom card lists in Magic: The Gathering Online. These files usually store data using the standard XML format.
Other software programs also use the .DEK extension. It can serve as an external package archive for Pure Data (managed by the Deken tool), which stores data as a compressed ZIP file. It can also act as a strategy game unit deck for the Eugen Systems Wargame series, a deck for Yugioh Virtual Desktop, or a draft declaration form in the Polish tax tool Przyjazne Deklaracje.
How to open DEK files?
You can open a Magic: The Gathering .DEK file directly in Magic: The Gathering Online or with third-party tools like the Cardhoarder Deck Editor. Because the .DEK extension has multiple possible meanings, we recommend using viewer.online/dek. This platform analyzes .DEK files to identify their exact format and creator software, shows which programs can open the file, and usually previews it.
If the file is an XML decklist, you can inspect it with simple text editors like Notepad or command-line tools. If the file is a Pure Data package, standard archive tools can extract the internal ZIP contents.
Best practices and troubleshooting
Always verify the source of your .DEK file. If a game fails to import the file, the internal structure might belong to a different software program. You can use a text editor to check the first few lines of the file. If you see readable text tags, it is likely an XML card decklist.
Summary
Because .DEK files use the known XML format, viewer.online/dek can safely open and display them online, eliminating compatibility problems. If your file actually contains compressed data or tax forms, the viewer will identify the actual format so you can find the right tool.