XLL files are a type of Excel file – specifically, an Excel Add-in file. They are used to accommodate add-ons and extensions that add functions to the software. XLL files are similar to DLL files but specifically created for Excel. They also share similarities with XLA and XLAM files – they too are third-party add-in file types.
How can you open XLL files?
Unsurprisingly, these files need to be opened with Microsoft Excel. Generally, double-clicking on the file should either automatically open it or open a window prompt where the user can select which program to use it with.
What programs work with XLL files?
Being a proprietary file format, they work best with Excel, however, you can also open them in a C/C++ editor, as that is the language they are written in.