ClosedXML

ClosedXML is a .NET library that enables users to read, manipulate and write Excel files. The idea behind the library is to provide an interface for dealing with the underlying tricky OpenXML API. The application is compatible with early versions of Excel 2007 and works with the newest releases as well. On the other hand, developers can manipulate the files without having to have Excel installed on their system.

It is important to note that the library is not thread-safe and hence, there is no guarantee that parallel operations would work. The utility comes with vast documentation and provides scenarios with the most likely situations, so users are advised to check the FAQ out.

For example, a common situation is when the text with numbers is converted to numbers. The reason behind this is that when the value property of a cell is set, the app calls the .ToString() method of the object and hence, interprets the value as a number, date, time stamp, boolean or text. Users who want to insert a number as text can address this issue by changing the cell's data type to text, setting the cell's format to “@” before setting the value or prepending a single quote character, like cell.Value = "'123", for instance.