Scaffold Skill — AutoCAD .NET Plugins

Agentic steps to create a new plugin project end-to-end. Execute these steps in order. All csproj patterns here are verified against AutoCAD 2027 / .NET 10.

Step 0 — Identify the target product

User says	Target	Template	Extra packages
"AutoCAD plugin" / "acad add-in"	AutoCAD 2027	acad	AutoCAD.NET 26.0.0
"Civil 3D plugin" / "c3d add-in"	Civil 3D 2027	civil	Civil3D.NET 13.9.628
"Plant 3D plugin" / "plant add-in"	Plant 3D 2027	(manual)	AutoCAD.NET.Core 26.0.0 + SDK DLL refs
"Design Automation" / "DA"	Any (headless)	acad	Use .Core + .Model only (no AcMgd)

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Step 1 — Scaffold

AutoCAD

dotnet new acad -n <ProjectName> -o <ProjectName>
cd <ProjectName>

Civil 3D

dotnet new civil --rootNamespace=<ProjectName> -o <ProjectName>
cd <ProjectName>

Plant 3D (manual)

Create <ProjectName>/<ProjectName>.csproj — see Plant 3D section below.

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Step 2 — Fix csproj (CRITICAL)

Templates may generate outdated or incorrect settings. Apply all of these fixes:

Target framework

If the template generated net8.0-windows or net6.0-windows, change to net10.0-windows.

Platform target — x64 preferred over RuntimeIdentifier

<!-- WRONG for most plugins — creates RID subfolder, assembly won't load in AutoCAD -->
<RuntimeIdentifier>win-x64</RuntimeIdentifier>

<!-- CORRECT — outputs to bin\Debug\net10.0-windows\ (no RID subfolder) -->
<PlatformTarget>x64</PlatformTarget>

Why: AutoCAD probes for assemblies in the direct output folder. RuntimeIdentifier creates a win-x64 subfolder that AutoCAD/accoreconsole doesn't search by default. Exception: If you are importing cross-platform native NuGet packages (like Oracle or SQLite), you do need <RuntimeIdentifier>win-x64</RuntimeIdentifier> to fetch the correct windows binaries. In this rare case, also add <AppendRuntimeIdentifierToOutputPath>false</AppendRuntimeIdentifierToOutputPath> to your csproj to prevent the output from being pushed into an unreachable subfolder.

GenerateTargetFrameworkAttribute

<GenerateTargetFrameworkAttribute>false</GenerateTargetFrameworkAttribute>

Prevents conflict with AutoCAD host's own TargetFramework attribute.

Reference csproj template — DA / Civil 3D headless

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Library</OutputType>
    <TargetFramework>net10.0-windows</TargetFramework>
    <PlatformTarget>x64</PlatformTarget>
    <RootNamespace>$(MSBuildProjectName)</RootNamespace>
    <Nullable>enable</Nullable>
    <GenerateTargetFrameworkAttribute>false</GenerateTargetFrameworkAttribute>
  </PropertyGroup>

  <ItemGroup>
    <FrameworkReference Include="Microsoft.WindowsDesktop.App" />
    <PackageReference Include="AutoCAD.NET.Core" Version="26.0.0" ExcludeAssets="runtime" />
    <PackageReference Include="AutoCAD.NET.Model" Version="26.0.0" ExcludeAssets="runtime" />
    <!-- Add Civil3D.NET for Civil 3D plugins -->
    <!-- <PackageReference Include="Civil3D.NET" Version="13.9.628" ExcludeAssets="runtime" /> -->
  </ItemGroup>
</Project>

Reference csproj template — Desktop-only (with UI)

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Library</OutputType>
    <TargetFramework>net10.0-windows</TargetFramework>
    <PlatformTarget>x64</PlatformTarget>
    <RootNamespace>$(MSBuildProjectName)</RootNamespace>
    <Nullable>enable</Nullable>
    <GenerateTargetFrameworkAttribute>false</GenerateTargetFrameworkAttribute>
  </PropertyGroup>

  <ItemGroup>
    <FrameworkReference Include="Microsoft.WindowsDesktop.App" />
    <PackageReference Include="AutoCAD.NET" Version="26.0.0" ExcludeAssets="runtime" />
  </ItemGroup>
</Project>

Plant 3D csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Library</OutputType>
    <TargetFramework>net10.0-windows</TargetFramework>
    <PlatformTarget>x64</PlatformTarget>
    <Nullable>enable</Nullable>
    <RootNamespace>$(MSBuildProjectName)</RootNamespace>
    <GenerateTargetFrameworkAttribute>false</GenerateTargetFrameworkAttribute>
  </PropertyGroup>

  <ItemGroup>
    <FrameworkReference Include="Microsoft.WindowsDesktop.App" />
    <PackageReference Include="AutoCAD.NET.Core" Version="26.0.0" ExcludeAssets="runtime" />
    <PackageReference Include="AutoCAD.NET.Model" Version="26.0.0" ExcludeAssets="runtime" />
  </ItemGroup>

  <!-- Plant 3D SDK — PLANT_SDK = path to inc-x64\ folder -->
  <!-- Download: https://aps.autodesk.com/developer/overview/autocad-plant-3d-objectarx-sdk-downloads -->
  <ItemGroup>
    <Reference Include="PnIDMgd">
      <HintPath>$(PLANT_SDK)\PnIDMgd.dll</HintPath>
      <Private>false</Private>
    </Reference>
    <Reference Include="PnPDataLinks">
      <HintPath>$(PLANT_SDK)\PnPDataLinks.dll</HintPath>
      <Private>false</Private>
    </Reference>
    <Reference Include="PnPDataObjects">
      <HintPath>$(PLANT_SDK)\PnPDataObjects.dll</HintPath>
      <Private>false</Private>
    </Reference>
    <Reference Include="PnPProjectManagerMgd">
      <HintPath>$(PLANT_SDK)\PnPProjectManagerMgd.dll</HintPath>
      <Private>false</Private>
    </Reference>
    <Reference Include="PnPCommonMgd">
      <HintPath>$(PLANT_SDK)\PnPCommonMgd.dll</HintPath>
      <Private>false</Private>
    </Reference>
    <Reference Include="PnPCommonDbxMgd">
      <HintPath>$(PLANT_SDK)\PnPCommonDbxMgd.dll</HintPath>
      <Private>false</Private>
    </Reference>
    <Reference Include="PnIdProjectPartsMgd">
      <HintPath>$(PLANT_SDK)\PnIdProjectPartsMgd.dll</HintPath>
      <Private>false</Private>
    </Reference>
  </ItemGroup>
</Project>

Set PLANT_SDK via Directory.Build.props:

<!-- Directory.Build.props (repo root) -->
<Project>
  <PropertyGroup>
    <PLANT_SDK Condition="'$(PLANT_SDK)'==''">D:\SDKS\Plant2027\inc-x64</PLANT_SDK>
  </PropertyGroup>
</Project>

---

Step 3 — Entry point boilerplate

Create App.cs (or verify template generated it):

using Autodesk.AutoCAD.Runtime;

[assembly: ExtensionApplication(typeof(<ProjectName>.App))]
[assembly: CommandClass(typeof(<ProjectName>.Commands))]

namespace <ProjectName>;

public class App : IExtensionApplication
{
    public void Initialize() { }
    public void Terminate() { }
}

---

Step 4 — Add launchSettings.json

Create Properties/launchSettings.json. Replace <ACAD_HOME> with the AutoCAD install path.

AutoCAD

{
  "profiles": {
    "<ProjectName>": { "commandName": "Project" },
    "AutoCAD2027": {
      "commandName": "Executable",
      "executablePath": "<ACAD_HOME>\\acad.exe"
    }
  }
}

Civil 3D

{
  "profiles": {
    "<ProjectName>": { "commandName": "Project" },
    "C3D2027_Metric": {
      "commandName": "Executable",
      "executablePath": "<ACAD_HOME>\\acad.exe",
      "commandLineArgs": "/ld \"<ACAD_HOME>\\AecBase.dbx\" /p \"<<C3D_Metric>>\" /product C3D /language en-US"
    },
    "C3D2027_Imperial": {
      "commandName": "Executable",
      "executablePath": "<ACAD_HOME>\\acad.exe",
      "commandLineArgs": "/ld \"<ACAD_HOME>\\AecBase.dbx\" /p \"<<C3D_Imperial>>\" /product C3D /language en-US"
    }
  }
}

Plant 3D

{
  "profiles": {
    "<ProjectName>": { "commandName": "Project" },
    "Plant3D2027": {
      "commandName": "Executable",
      "executablePath": "<ACAD_HOME>\\acad.exe",
      "commandLineArgs": "/product PLNT3D /language \"en-US\""
    }
  }
}

---

Step 5 — Build and load

dotnet build -c Debug

Output: bin\Debug\net10.0-windows\<ProjectName>.dll

Desktop: In AutoCAD, use NETLOAD to load the DLL (see Step 5a). accoreconsole: Use .scr script with SECURELOAD 0 then NETLOAD, or use /al (see Step 6).

---

Step 5a — Desktop UI testing (NETLOAD)

First-time load

1. Launch AutoCAD (or Civil 3D / Plant 3D) via the launchSettings profile or directly
2. At the command line: NETLOAD
3. Browse to bin\Debug\net10.0-windows\<ProjectName>.dll
4. Run your command (e.g., MYCOMMAND)

SECURELOAD handling

AutoCAD defaults to SECURELOAD=1 which blocks DLLs from untrusted paths. Options:

Approach	When to use
SECURELOAD 0 at command line	Quick one-off testing — reset per session
TRUSTEDPATHS sysvar	Add your build output folder to the trusted list (persists in registry)
TRUSTEDLOCATIONS dialog	UI version of TRUSTEDPATHS — Settings > Files > Trusted Locations

To add a trusted path programmatically:

TRUSTEDPATHS

Append ;C:\your\build\output\path to the existing value.

Auto-load on startup (without ApplicationPlugins bundle)

For repeated testing, avoid typing NETLOAD every launch. Add to the Startup Suite:

1. APPLOAD command
2. Click "Contents..." under Startup Suite
3. Add your DLL

Or use acad.lsp / acaddoc.lsp in the support path:

;; acaddoc.lsp — runs on every document open
(command "NETLOAD" "C:\\path\\to\\Plugin.dll")

Debugging with Visual Studio / VS Code

With launchSettings.json configured (Step 4):

1. Set breakpoints in your code
2. Start debugging (F5) — AutoCAD launches with the selected profile
3. In AutoCAD: NETLOAD your DLL, then run your command
4. Breakpoints hit in VS

For attach-to-process (when AutoCAD is already running):

• Debug > Attach to Process > select acad.exe

---

Step 6 — Local testing with accoreconsole (headless)

Method A: NETLOAD via script

Create a .scr script file:

SECURELOAD
0
NETLOAD
C:\full\path\to\Plugin.dll
MYCOMMAND

Launch:

accoreconsole.exe /i "drawing.dwg" /s "test.scr" /ld "AecBase.dbx" /product C3D /language en-US

Method B: /al with .bundle (recommended)

Matches DA behavior more closely. Create a bundle folder structure:

TestBundle/
  <ProjectName>.bundle/
    PackageContents.xml
    Contents/
      <ProjectName>.dll
      <ProjectName>.deps.json

The .scr only needs the command (no SECURELOAD/NETLOAD):

MYCOMMAND

Launch:

accoreconsole.exe /i "drawing.dwg" /al "TestBundle" /s "test.scr" /isolate user1 "D:\Tmp" /ld "AecBase.dbx" /product C3D /language en-US

Rules:

• /al points to the parent of the .bundle folder
• Always use /isolate to prevent registry writes into your working directory
• See autocad-api.md for full flag reference.

---

Step 7 — ApplicationPlugins Bundle (desktop auto-load)

For desktop deployment (not DA), place a .bundle folder in one of these paths:

Path	Scope	Requires admin
%APPDATA%\Autodesk\ApplicationPlugins\	Current user	No
C:\Program Files\Autodesk\ApplicationPlugins\	All users	Yes

AutoCAD scans these on startup and loads any .bundle with a valid PackageContents.xml.

Minimal bundle for a .NET plugin

%APPDATA%\Autodesk\ApplicationPlugins\
  <ProjectName>.bundle/
    PackageContents.xml
    Contents/
      <ProjectName>.dll
      <ProjectName>.deps.json

PackageContents.xml with command registration

<?xml version="1.0" encoding="utf-8" ?>
<ApplicationPackage SchemaVersion="1.0" Version="1.0.0"
  ProductCode="{generate-new-guid}"
  Name="<ProjectName>"
  Description="..."
  Author="...">
  <CompanyDetails Name="..." Url="..." Email="..." />
  <RuntimeRequirements
    Platform="AutoCAD"
    SeriesMin="R26.0" SeriesMax="R26.0"
    OS="Win64" />
  <Components Description="plugin">
    <RuntimeRequirements
      SupportPath="./Contents"
      Platform="AutoCAD"
      SeriesMin="R26.0" SeriesMax="R26.0"
      OS="Win64" />
    <ComponentEntry
      AppName="<ProjectName>"
      AppType=".NET"
      Version="1.0.0"
      ModuleName="./Contents/<ProjectName>.dll"
      AppDescription="..."
      LoadOnAutoCADStartup="True"
      LoadOnCommandInvocation="False">
      <Commands GroupName="<ProjectName>_Commands">
        <Command Local="MYCOMMAND" Global="MYCOMMAND" />
      </Commands>
    </ComponentEntry>
  </Components>
</ApplicationPackage>

Key attributes:

• Platform: AutoCAD (base), Civil3D, Plant3D, or pipe-delimited AutoCAD|Civil3D
• SeriesMin/SeriesMax: R26.0 = 2027, R25.1 = 2026, R25.0 = 2025
• LoadOnAutoCADStartup="True": loads DLL immediately on startup
• LoadOnCommandInvocation="True" + LoadOnAutoCADStartup="False": deferred load (only when command is invoked)
• SupportPath="./Contents": adds Contents folder to AutoCAD's support file search path
• <Commands>: registers commands so AutoCAD knows which bundle to load on demand

Build script to deploy bundle locally

$BundleName = "<ProjectName>"
$BuildOut = "bin\Debug\net10.0-windows"
$BundleDest = "$env:APPDATA\Autodesk\ApplicationPlugins\$BundleName.bundle"

# Create bundle structure
New-Item "$BundleDest\Contents" -ItemType Directory -Force | Out-Null
Copy-Item "PackageContents.xml" "$BundleDest\" -Force
Copy-Item "$BuildOut\$BundleName.dll" "$BundleDest\Contents\" -Force
Copy-Item "$BuildOut\$BundleName.deps.json" "$BundleDest\Contents\" -Force

Write-Host "Deployed to: $BundleDest"

Restart AutoCAD after deploying. The bundle loads automatically.

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Step 8 — DA Bundle Packaging

PackageContents.xml

<?xml version="1.0" encoding="utf-8" ?>
<ApplicationPackage SchemaVersion="1.0" Version="1.0.0"
  ProductCode="{generate-new-guid}"
  Name="<ProjectName>"
  Description="..."
  Author="...">
  <CompanyDetails Name="..." Url="..." Email="..." />
  <Components Description="plugin">
    <RuntimeRequirements
      SeriesMin="R26.0" SeriesMax="R26.0"
      Platform="AutoCAD"
      OS="Win64" />
    <ComponentEntry
      AppName="<ProjectName>"
      Version="1.0.0"
      ModuleName="./Contents/<ProjectName>.dll"
      AppDescription="..."
      LoadOnAutoCADStartup="True"
      LoadOnCommandInvocation="False" />
  </Components>
</ApplicationPackage>

SeriesMin/SeriesMax: R26.0 = AutoCAD 2027. Must match the DA engine version.

Bundle folder structure

<ProjectName>.bundle/
  PackageContents.xml
  Contents/
    <ProjectName>.dll
    <ProjectName>.deps.json

Zip correctly (CRITICAL)

# CORRECT — bundle folder is zip root
Compress-Archive -Path "$ProjectName.bundle" -DestinationPath "$ProjectName.zip"

# WRONG — puts PackageContents.xml at zip root; bundle silently not loaded
Compress-Archive -Path "$ProjectName.bundle\*" -DestinationPath "$ProjectName.zip"

DA Activity commandLine

$(engine.path)\accoreconsole.exe /i "$(args[inputFile].path)" /al "$(appbundles[<BundleName>].path)" /s "$(settings[script].path)"

• /al loads a .bundle from a parent folder (see below for local usage)
• /s passes the script with command invocations

Using /al locally with accoreconsole (undocumented)

/al works in desktop accoreconsole too -- it is just not in the official docs. The argument is the parent folder containing the .bundle directory:

TestFolder/
  MyPlugin.bundle/
    PackageContents.xml
    Contents/
      MyPlugin.dll

Launch:

accoreconsole.exe /i "drawing.dwg" /al "D:\TestFolder" /s "test.scr" /isolate user1 "D:\Tmp"

Rules:

• /al points to the parent of the .bundle folder, not the bundle itself
• Always use /isolate -- without it, /al writes registry entries into the parent folder which pollute your working directory
• /isolate user1 <tempDir> redirects those registry writes to a temp directory
• The .scr script does NOT need SECURELOAD 0 or NETLOAD when using /al -- the bundle is loaded automatically

DA Engine IDs (use + not .)

Product	Engine ID
AutoCAD 2027	Autodesk.AutoCAD+26_0
AutoCAD 2026	Autodesk.AutoCAD+25_1
AutoCAD 2025	Autodesk.AutoCAD+25_0

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Verified Build Output Path

After dotnet build -c Debug with the correct csproj settings:

bin\Debug\net10.0-windows\<ProjectName>.dll     ← load this
bin\Debug\net10.0-windows\<ProjectName>.deps.json
bin\Debug\net10.0-windows\<ProjectName>.pdb

If you see bin\Debug\net10.0-windows\win-x64\ subfolder, you have RuntimeIdentifier in your csproj without the proper overrides. Remove it and use PlatformTarget, or set <AppendRuntimeIdentifierToOutputPath>false</AppendRuntimeIdentifierToOutputPath>.