Step 1: Define the problem precisely
Write down what the engineer does today, step by step, and what the plugin should do instead. Collect real sample files, including messy ones. A clear definition prevents most project problems later.
Step 2: Choose the platform and API
Most modern desktop CAD plugins are written in C# on .NET, because AutoCAD, Inventor, Revit and SOLIDWORKS all provide .NET APIs. C++ is used where performance or deep access is needed (ObjectARX, Creo TOOLKIT, CATIA CAA). Python is common for Fusion and NX Open.
| CAD | Typical plugin type | Language |
|---|---|---|
| AutoCAD | .NET assembly loaded by NETLOAD or autoloader bundle | C# |
| Inventor | Add-in registered with an .addin manifest | C# |
| Revit | External command / application with .addin manifest | C# |
| SOLIDWORKS | COM add-in implementing ISwAddin | C# |
| Fusion | Script or add-in | Python / C++ |
Step 3: Set up the project
- Install the matching CAD version and its SDK or API references.
- Target the .NET version required by that CAD release.
- Reference the API assemblies without copying them to the output folder.
- Configure debugging to launch the CAD application.
Step 4: Write your first command
Here is a minimal AutoCAD .NET command that counts the block references in the current drawing:
using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.Runtime;
public class Commands
{
[CommandMethod("COUNTBLOCKS")]
public void CountBlocks()
{
Document doc = Application.DocumentManager.MdiActiveDocument;
int count = 0;
using (Transaction tr = doc.Database.TransactionManager.StartTransaction())
{
var ms = (BlockTableRecord)tr.GetObject(
SymbolUtilityServices.GetBlockModelSpaceId(doc.Database), OpenMode.ForRead);
foreach (ObjectId id in ms)
if (id.ObjectClass.DxfName == "INSERT") count++;
tr.Commit();
}
doc.Editor.WriteMessage($"\nBlock references: {count}");
}
}Step 5: Build the user interface
Add a ribbon tab and buttons so users never need to type commands. Use dialogs (WPF or WinForms) for inputs and dockable palettes for tools that stay open. Match the look of the host application.
Step 6: Handle errors and undo
Wrap changes in transactions, validate inputs, and report problems clearly. A plugin must never leave a model half-modified.
Step 7: Test with real data
Test with large assemblies, old files, missing references and different units. Then run a pilot with a few engineers and fix what they find.
Step 8: Package and deploy
- Create an installer (MSI or Autodesk bundle format) that registers the plugin.
- Store settings in a shared configuration file, not in the code.
- Add licensing if you sell the plugin, and logging for support.
- Plan updates for every new CAD release.
A plugin is a product, not a script. Treat installation, updates and support as part of the build.
Need a plugin built?
ENGIMANDI builds CAD plugins end to end, from specification to installer and yearly updates. See our CAD customisation services or chat with us on WhatsApp +91-9677261485.