.XLL File Extension

Microsoft Excel Add-in

Developer Microsoft
3.5  |  35 Votes

What is an XLL file?

An XLL file is an add-in used by Microsoft Excel, a popular spreadsheet application. It contains extra functions, templates, or other tools that enhance the capabilities of Excel. Examples of add-ins include custom chart generators and template managers.

More Information

The XLL file type was introduced in 1996 with the release of Microsoft Excel 97. It is saved in the same format as the Dynamic Link Library (.DLL) file type but is renamed with the .xll file extension to indicate its association with Excel.

XLL files are similar to .XLA and .XLAM add-in files in that they both provide functionality that extends the capabilities of Excel. However, XLA and XLAM files are written in the Visual Basic for Applications (VBA) programming language and XLL files are written in the C/C++ programming language. While Microsoft develops some add-ins, third-party software developers developed most of them.

How to open an XLL file

XLL files are not meant to be directly opened. Instead, you can install an XLL file in Microsoft Excel to add capabilities to the application. To install an XLL file:

  1. Select File → Options → Add-Ins.
  2. In the Manage dropdown menu, select Excel Add-ins, then click Go.
  3. In the Add-Ins window, select Browse..., then choose the XLL file you would like to install.


While XLL files are typically legitimate Microsoft Excel add-ins, they can also be used to distribute and execute malware attacks on victims' computers. To protect against malware attacks, do not double-click or install an XLL file unless you trust the file's source.

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