How do you set up Visual Studio Code for C# and .NET development, and what do the C# extension and C# Dev Kit each provide?

1. The pieces and how they talk

VS Code (UI process)
   |  JSON-RPC over the Language Server Protocol
   v
Roslyn language server --> MSBuild design-time evaluation of each .csproj
   |                          (references, analysers, source generators,
   |                           compiler options per target framework)
   v
completions, diagnostics, code fixes, Go to Definition

C# Dev Kit --> Solution Explorer, project system, Test Explorer (runs tests through the SDK)
Debugger   <-- launch.json, or launchSettings.json profiles via C# Dev Kit
.NET Install Tool --> downloads runtimes the extensions themselves need

The extensions do not install the .NET SDK you build with. They use the SDK that dotnet resolves for the workspace folder, which honours global.json.

2. How a workspace loads

1. VS Code opens the folder. C# Dev Kit looks for solution files (.sln, .slnx) or projects. With several solutions, dotnet.defaultSolution in .vscode/settings.json decides which one loads.
2. The language server runs dotnet restore if needed, then a design-time build per project and target framework.
3. Diagnostics appear in the Problems panel; load errors appear in View → Output → C# (and C# Dev Kit).

If IntelliSense is empty or wrong, the cause is almost always in steps 1–2: wrong SDK, failed restore (often a private feed needing credentials), or the wrong solution loaded. .NET: Restart Language Server reloads after you fix it.

3. Debugging in depth

launch.json describes debug sessions:

tasks.json defines commands. The $msCompile problem matcher turns compiler output into clickable Problems entries.

With C# Dev Kit you can also skip launch.json: choose Run and Debug → C# and pick a project; for ASP.NET Core it launches from Properties/launchSettings.json profiles, which Visual Studio, Rider and dotnet run share.

4. Licensing in practice

Teams that can't use C# Dev Kit can still use the C# extension alone: IntelliSense and debugging work, but there is no Solution Explorer or Test Explorer.

5. Remote and container development

The Remote – SSH, WSL and Dev Containers extensions run the language server and debugger on the remote machine or in the container, while the UI stays local. The SDK, extensions and NuGet cache live where the code lives, which gives a reproducible Linux toolchain for every developer.

6. Performance

• Large solutions: open a sub-folder or set dotnet.defaultSolution to a smaller solution or solution filter.
• Analysers and source generators run in the language server; a slow generator makes typing slow.
• Exclude bin/ and obj/ from file watching (files.watcherExclude) in very large repos.

7. Security

Workspace Trust opens unfamiliar folders in Restricted Mode, which disables tasks, debugging and some extension features until you trust the folder. Keep it on: a cloned repo's tasks.json can run any command. Install only extensions from trusted publishers, and use .vscode/extensions.json to recommend the approved set.

8. Try it yourself

1. Install C# Dev Kit and run dotnet new webapi -n Api -o src/Api.
2. Add the launch.json and tasks.json from the code example and press F5.
3. Set a breakpoint in an endpoint, call it, and inspect variables.
4. Remove launch.json, use Run and Debug → C# instead, and compare.
5. Add extensions.json, reopen the folder on another machine and accept the recommendation prompt.
6. Break restore on purpose (add a non-existent package) and find the error in the C# output pane.

Install the extension from the command line:

code --install-extension ms-dotnettools.csdevkit

.vscode/extensions.json, committed so teammates get a prompt:

{
  "recommendations": [
    "ms-dotnettools.csdevkit",
    "editorconfig.editorconfig"
  ]
}

.vscode/tasks.json:

{
  "version": "2.0.0",
  "tasks": [
    {
      "label": "build",
      "type": "process",
      "command": "dotnet",
      "args": ["build", "${workspaceFolder}/src/Api/Api.csproj"],
      "problemMatcher": "$msCompile"
    }
  ]
}

.vscode/launch.json:

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Launch Api",
      "type": "coreclr",
      "request": "launch",
      "preLaunchTask": "build",
      "program": "${workspaceFolder}/src/Api/bin/Debug/net10.0/Api.dll",
      "cwd": "${workspaceFolder}/src/Api",
      "env": { "ASPNETCORE_ENVIRONMENT": "Development" },
      "stopAtEntry": false
    }
  ]
}