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C# Scripts

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Use C# scripts when you want a short typed snippet without creating a full add-in project.

Entry suffix:

*script.csx

Example​

Pick an element and trace its bounding box. In Revit the traced box is drawn in the active view:

bbox_script.csx
#r "C:/Program Files/Autodesk/Revit 2025/RevitAPI.dll"
#r "C:/Program Files/Autodesk/Revit 2025/RevitAPIUI.dll"

using System.Diagnostics;
using Autodesk.Revit.Attributes;
using Autodesk.Revit.DB;
using Autodesk.Revit.UI;
using Autodesk.Revit.UI.Selection;

[Transaction(TransactionMode.Manual)]
public class BoundingBoxCommand : IExternalCommand
{
    public Result Execute(ExternalCommandData commandData, ref string message, ElementSet elements)
    {
        var uidoc = commandData.Application.ActiveUIDocument;
        var reference = uidoc.Selection.PickObject(ObjectType.Element);
        var element = uidoc.Document.GetElement(reference);

        Trace.Write(element.get_BoundingBox(null));
        return Result.Succeeded;
    }
}

A fuller script with a shared helper and a task dialog is in the repo: main_script.csx.

NuGet References​

Declare package references with Roslyn #r directives:

#r "nuget: Newtonsoft.Json, 13.0.3"
#r "C:/Program Files/Autodesk/Revit 2025/RevitAPI.dll"
#load "./Helpers/DocumentHelper.csx"

#r "nuget: …" restores packages automatically into %APPDATA%\RevitDevTool\nuget. Paths to host API assemblies are adjusted for the running host.

Package resolution

Scripts resolve NuGet packages for you, so a .csx needs no project file. Versioning, conflicts with host assemblies and restore problems are covered in NuGet Dependencies.

#load pulls additional .csx files into the script graph. Each file can declare its own #r and #load directives.

Host Version Symbols​

Scripts receive the same preprocessor symbols as host add-in projects (REVIT2025, REVIT2025_OR_GREATER, AUTOCAD2026, and so on). Use #if REVIT2025_OR_GREATER in .csx the same way you would in a compiled add-in.

For example, one script can handle an API that changed between Revit versions, and tell Revit from AutoCAD:

version_script.csx
#if REVIT2024_OR_GREATER
Trace.WriteLine(element.Id.Value);          // ElementId.Value is a long since Revit 2024
#else
Trace.WriteLine(element.Id.IntegerValue);   // older versions use an int
#endif

#if REVIT
Trace.WriteLine("Running in Revit");
#elif AUTOCAD
Trace.WriteLine("Running in AutoCAD");
#endif

The symbols are chosen from the host and year that run the script, so the same file works on every supported version.

Debugging​

An attached debugger binds breakpoints directly to your original .csx files.

Workflow:

  1. Open the script folder in Visual Studio or VS Code (C# Dev Kit recommended).
  2. Set breakpoints in your .csx files.
  3. Attach the debugger to the running host process (Revit.exe, acad.exe, …).
  4. Run the script from RevitDevTool.

For attach settings shared with F# scripts and assemblies, see Attach Debugger.

Samples​