Software & Apps File Types What Is an XLL File? How to open, edit, and convert XLL files by Tim Fisher General Manager, VP, Lifewire.com Tim Fisher has 30+ years' professional technology support experience. He writes troubleshooting content and is the General Manager of Lifewire. our editorial process Facebook Twitter LinkedIn Tim Fisher Updated on September 11, 2020 File Types Design Cryptocurrency MS Office Windows Linux Google Drive Apps File Types Backup & Utilities View More Tweet Share Email A file with the XLL file extension is an Excel Add-in file. These files provide a way to use third-party tools and functions in Microsoft Excel that aren't natively part of the software. Excel Add-in files are similar to DLL files except that they're built specifically for Excel. XLL Files. How to Open an XLL File XLL files can be opened with Microsoft Excel. If double-clicking an XLL file doesn't open it in Excel, you can do it manually via the File > Options menu. Select the Add-ins category and then choose Excel Add-ins in the Manage drop-down box. Choose the Go button and then Browse to locate it. If you still can't get the file to work with Excel, Microsoft has some more information on Excel add-ins that might be helpful. If a program on your computer tries to open the file but it's not Excel, you can change the default program that handles XLL files. There are very few, if any, other formats that also utilize this file extension, so this probably won't happen to you, but it's worth recognizing. How to Convert an XLL File We're not aware of a file converter or other tool that can save XLL files to any other format, or why you would need to. If it does something in Excel that you'd like it to do elsewhere, in another program, you'll instead need to look at redeveloping the abilities that the XLL provides, not just "converting" it to some other format. XLL vs XLA/XLAM Files XLL, XLA, and XLAM files are all Excel Add-in files, but there are some key differences between them. For most people, it makes no difference which add-in file type is installed, but you might take note if you're building one of these add-ins yourself. XLAM files are just XLA files that can contain macros. They also differ from XLA in that they use XML and ZIP to compress data. To start, XLA/XLAM files are written in VBA while XLL files are written in C or C++. This means the add-in is compiled and more difficult to crack or manipulate, which can be a good thing, depending on your perspective. XLL files are also superior in that they're like DLL files, which means Excel can use them much like it uses its other built-in controls. Due to the VBA code that XLA/XLAM files are written in, they have to be interpreted in a different way each time they're run, which can result in slower executions. However, XLA and XLAM files are easier to build because they can be created from within Excel and saved to an .XLA or .XLAM file, while XLL files are programmed using the C/C++. programming language. Building XLL Files Some Excel Add-ins are included with Excel right out of the box, but you can also build your own using Microsoft's free Visual Studio Express software. You'll find lots of specific instructions from CodePlex and Add-In-Express. Still Can't Open It? If you can't open the file after using the suggestions from above, make sure that you're actually dealing with an Excel Add-in file and not something that just uses a similar file extension. For example, an XL file is also an Excel file but it's used as a spreadsheet. They also open with Excel but not through the method described above for XLL files. They instead are used like XLSX and XLS files. XLR files are similar but are actually related to the Words Spreadsheet or Charts file format, a format that's similar to Excel's XLS. If you check the file extension and you don't have an XLL file, then research that suffix to see how to open it or convert the file to a different file format for use in a specific program.