XLL, Excel Add-In File (.xll)
The XLL Misc file format
XLL files are used by the Microsoft Office suite program Excel, a spreadsheet program that runs on Windows but is also available for Mac computers. This binary file contains information about the extension of Excel, such as extra functions, templates and other tools that add to the usage of the software.
Technical details of XLL files
XLL files, while used by Excel, do not contain any spreadsheet data. Instead, the file contains information about plugins for Microsoft Excel. The files are comparable to DLL files, yet they have been developed specifically for the Microsoft spreadsheet program.