This is an open source project that lets you create native (.xll) add-ins for Excel using C#, VB.Net or F#.
The advantage of an XLL add-in is that it can contain high performance user-defined functions, custom ribbon interfaces plus more and requires no installation or registration and therefore working in reduced privilege environments.
The C API is not directly accessible from .NET code but the Excel-DNA runtime allows managed assemblies to integrate with the C API.
You are able to define the function wizard category as well as the function description and argument descriptions.
In Excel-DNA this is made possible by adding .NET attributes to the function declarations.
Other Supported Features
Custom Task Panes
Integration with VBA code
The Excel-DNA runtime contains a small loader (the .XLL) that loads the .NET runtime, then checks the configuration (.dna) file and accordingly loads the managed assembly.
The managed assemblies are then inspected using the .NET Reflection API and the appropriate methods are registered.
Create Basic Add-in
This consists of three files:
1) The managed assembly MyCSharpCode.dll
2) The Excel-DNA runtime library. Distributed as exceldna.xll but renamed to MyFirstAddin.xll
3) A configuration file which is a text-based XML file renamed to MyFirstAddin.dna which contains the following:
<DnaLibrary Name="My First AddIn" RuntimeVersion="v4.0" >
public class MyClass
public static string MyFunction([ExcelArgument(Description=@"Text Value")] string sText)
return sText + sText;
AutoOpen and AutoClose
These methods will be called when your add-in is loaded and unloaded from the Excel Add-ins dialog box
public void AutoOpen()
public void AutoClose()
Excel-DNA also contains a special packing feature that allows you to create a single xll file containing all the necessary files.