ObjectARX

Short answer

Autodesk's C++ runtime extension SDK for AutoCAD. The lowest-level, highest-performance way to extend AutoCAD.

ObjectARX (AutoCAD Runtime eXtension) is the C++ SDK for building AutoCAD plugins. ARX modules are unmanaged DLLs renamed .arx that load directly into the AutoCAD process — they bypass the .NET wrapper and run at native speed, which is why heavy custom-entity work and reactors that fire per-redraw are usually written in ObjectARX. The trade-off is that ARX is version-locked: a plugin built against ObjectARX 2024 won't load in AutoCAD 2025 without a rebuild.

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AutoCAD .NET Plugins (C# / VB.NET)

Verified .NET plugins for AutoCAD and the AutoCAD verticals. NETLOAD-ready DLLs and one-click .bundle installers, with explicit AutoCAD version compatibility on every listing.

Related terms

.NET plugin

A managed assembly (C#/VB.NET DLL) that uses Autodesk's .NET API to add commands and behaviour to AutoCAD or Civil 3D.

NETLOAD

The AutoCAD command that loads a managed .NET plugin DLL into the running session.