Cardmarket Helper is a Firefox extension designed to enhance the shopping experience on Cardmarket, a platform for trading card enthusiasts. This subscription-based tool provides a suite of features that streamline the process of managing card collections and sales. Users can easily upload their ManaBox CSV files and access them across various Cardmarket pages, view details for specific card printings, and quickly fill out sell forms with just one click.

In addition to improving user efficiency, Cardmarket Helper offers valuable insights by displaying format legality and MTGTop8 play-rate data directly on the Offers and Singles pages. The extension also features price comparisons against Cardmarket's low, average, and trend prices, allowing users to make informed decisions. With options to export and import lists, manage sales orders, and receive in-page notifications for updates, Cardmarket Helper is an essential tool for any serious card trader.