What Is an XLL File?

How to open, edit, and convert XLL files

XLL files in a Windows 10 folder
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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 Microsoft Excel.

How to Open an XLL File

XLL files can be opened with Microsoft Excel.

If double-clicking on an XLL file doesn't open it in MS 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 the XLL file.

XLL file in Excel

If you still can't get the XLL 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 an XLL file but it's not Excel, you can change the default program for a specific file extension. There are very few, if any, other formats that also utilize the XLL extension, so this probably won't happen to you, but it's worth recognizing.

How to Convert an XLL File

We're not currently aware of a file converter or other tool that can save XLL files to any other format, or why you would need to.

If an XLL file 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 with, XLA/XLAM files are written in VBA while XLL files are written in C or C++. This means the XLL 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 Microsoft 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 Microsoft Excel right out of the box, but you can also build your own Excel Add-in file using Microsoft's free Visual Studio Express software.

You'll find lots of specific instructions from Microsoft, CodePlex, and Add-In-Express.

Still Can't Open Your File?

If you can't open the XLL 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 that stores data within rows and columns that are made up of cells. XL files also open with Excel but not through the method described above for XLL files. XL files open like regular Excel files like XLSX and XLS files.

XLR files are similar in that its file extension looks an awful lot like ".XLL" but is 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.