Skip to main content

VS Code to Cursor Migration: Fixing Missing Extensions (C++, C# DevKit)

 You made the jump. You installed Cursor, imported your VS Code settings, and prepared to experience the AI-first workflow. But the moment you opened your .NET or C++ project, the excitement stalled. The Solution Explorer is missing, IntelliSense is acting like basic text completion, and your code . muscle memory feels wasted.

If you are looking for the "C# DevKit" or the official "C/C++" extension in the Cursor extension marketplace, they are likely missing or refusing to install.

This is not a bug in Cursor; it is a licensing and marketplace architecture conflict. This guide details the root cause of these missing tools and provides the technical steps to restore your C# and C++ development environment to full functionality.

The Root Cause: Open VSX vs. Visual Studio Marketplace

To fix the problem, you must understand how VS Code forks handle extensions.

Visual Studio Code (the open-source product) and VS Code (the Microsoft product) are distinct. When you use Cursor, you are using a fork of the open-source base. Microsoft’s Visual Studio Marketplace is proprietary. While Microsoft allows VS Code to access it, most forks—including VSCodium and Cursor—default to the Open VSX Registry, an open-source alternative maintained by the Eclipse Foundation.

The Licensing Wall

The specific extensions causing you pain—C# DevKit and Microsoft C/C++ (cpptools)—are proprietary.

  1. Distribution: Microsoft does not publish these to Open VSX.
  2. Licensing: The license terms for C# DevKit and the C++ debugger often explicitly state they may only be used with "Visual Studio products."
  3. DRM: Newer versions of C# DevKit require a Microsoft account login and perform a check to ensure they are running in an "official" environment.

Cursor has done significant work to bridge this gap, but automatic imports often fail for these proprietary binaries. We have to bypass the Open VSX search and manually inject the official binaries.

The Fix: Sideloading VSIX Binaries

The most reliable method to get these extensions working is "VSIX Sideloading." This bypasses the search registry entirely and installs the compiled extension package directly.

Step 1: Download the Extension Package

Do not download these through Cursor. You must navigate to the Visual Studio Marketplace via a web browser to get the official source files.

  1. For C# DevKit: Visit the C# DevKit Marketplace Page.
  2. For C++: Visit the C/C++ Marketplace Page.
  3. For C# (Base): Visit the C# Base Extension Page.

On the right-hand sidebar of each page, look for the "Download Extension" link. This will download a .vsix file to your computer.

Step 2: Manual Installation in Cursor

Once you have the .vsix files:

  1. Open Cursor.
  2. Open the Command Palette (Ctrl+Shift+P or Cmd+Shift+P).
  3. Type and select: Extensions: Install from VSIX...
  4. Navigate to your downloads folder and select the .vsix file you just downloaded.
  5. Restart Cursor immediately after installation.

Step 3: Verifying the C# DevKit Activation

C# DevKit is unique because it requires a "Solution Explorer" view that is not native to the core VS Code open-source build.

  1. Open a .sln or .csproj file.
  2. Look at the bottom right status bar. You should see a notification: "C# DevKit: Signing in..."
  3. If prompted, complete the Microsoft authentication flow.
  4. Once signed in, click the Cursor icon in the Activity Bar (left side), then look for the Solution Explorer pane (it may appear as a generic file icon or a separate .NET icon depending on the version).

The "Principal Engineer" Approach: Better Alternatives

While sideloading works, relying on proprietary extensions that fight against your editor's nature is a fragility risk. If C# DevKit updates and introduces stricter DRM, your workflow breaks.

For a rigorous, long-term setup, consider these high-performance alternatives that are native to the open-source ecosystem.

Alternative 1: The "Legacy" C# Configuration

If C# DevKit (which is relatively new) feels bloated or fails to load your projects, you can revert to the standard OmniSharp-powered experience. This is often faster and more stable for pure code editing.

  1. Uninstall C# DevKit.
  2. Install the standard C# extension (via the VSIX method above if missing).
  3. Modify your settings.json in Cursor to force the use of OmniSharp instead of the modern language server protocol if you encounter issues.
{
  "dotnet.server.useOmnisharp": true,
  "omnisharp.useModernNet": true,
  "omnisharp.organizeImportsOnFormat": true
}

Alternative 2: clangd for C++ (Superior Performance)

The Microsoft C++ extension is notorious for being heavy and slow on large codebases. The industry standard for high-performance C++ tooling is clangd (part of the LLVM project). It is open source, significantly faster, and fully compatible with Cursor via Open VSX.

Why switch?

  • Lower memory footprint.
  • Instant go-to-definition.
  • Better understanding of complex C++ templates.

Migration Steps:

  1. Disable the Microsoft C/C++ Extension.
  2. Search for and install clangd in the Cursor marketplace (no sideloading required).
  3. Generate a compilation database for your project. If you use CMake, run:
    cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=1 .
  4. Configure clangd in your settings.json to handle headers correctly:
{
    "clangd.arguments": [
        "--background-index",
        "--clang-tidy",
        "--header-insertion=iwyu",
        "--completion-style=detailed",
        "--function-arg-placeholders"
    ],
    "clangd.fallbackFlags": [
        "-std=c++20"
    ]
}

Troubleshooting & Edge Cases

Issue: "Extension is not compatible with this version of VS Code"

Cursor runs on a specific version of the VS Code engine (e.g., 1.86). If you download the absolute latest VSIX, it might demand version 1.90+.

The Fix:

  1. In Cursor, go to Help > About and note the "Commit" or base VS Code version.
  2. On the Visual Studio Marketplace page, click the Version History tab.
  3. Download a VSIX version released around the same date as your Cursor build version.

Issue: C# DevKit "Project Failed to Load"

If the extension installs but projects stay red/unloaded:

  1. Ensure you have the .NET SDK installed globally via your terminal (dotnet --version). C# DevKit does not bundle the SDK; it only bundles the runtime for the extension itself.
  2. Check the output logs. Open the Output panel (Ctrl+Shift+U) and switch the dropdown to C# DevKit or Project System Tools.

Conclusion

Migrating to Cursor allows you to leverage powerful AI features, but it requires navigating the fragmented landscape of VS Code extensions. By manually sideloading the official .vsix files for C# and C++, you can bypass marketplace restrictions.

However, for C++ developers specifically, take this opportunity to evaluate clangd. It aligns better with the Cursor ethos: modern, fast, and open. For .NET developers, sideloading C# DevKit is currently the necessary bridge to keep your Solution Explorer intact.

Labels: