Duplicate Preventer is a Microsoft Excel add-in that helps to prevent entering duplicate data while working in Excel. Duplicate Preventer integrates into MS Excel by placing its toolbar into the Excel toolbar area. The add-in allows defining where to check for duplicates in the active row, column or only in a selected area. The duplicate tracking is optionally possible with exactly the same data and data within different letter cases. Defined tracking options save and activate in one click when required.