Anatomy of an extension

After creating your first extension, let's understand the key parts of the project.

Project structure

A typical VisualStudio.Extensibility extension project looks like this:

MyExtension/
├── MyExtension.csproj
├── ExtensionEntrypoint.cs      ← Extension class (entry point)
├── Commands/
│   └── Command1.cs             ← Command handlers
├── ToolWindows/                ← Tool window definitions
├── .vsextension/
│   └── string-resources.json   ← Localized strings
└── bin/Debug/.vsextension/
    └── extension.json          ← Generated build output (metadata)

The Extension class

Every extension has one class that inherits from Extension. This is your entry point:

[VisualStudioContribution]
internal class ExtensionEntrypoint : Extension
{
    public override ExtensionConfiguration ExtensionConfiguration => new()
    {
        Metadata = new(
            id: "MyExtension.abc123",
            version: this.ExtensionAssemblyVersion,
            publisherName: "My Company",
            displayName: "My Extension"),
    };
}

The [VisualStudioContribution] attribute tells Visual Studio this class exists and should be loaded.

Commands

Commands are the most common contribution. Each command is a class:

[VisualStudioContribution]
internal class MyCommand : Command
{
    public override CommandConfiguration CommandConfiguration => new("My Command")
    {
        Placements = [CommandPlacement.KnownPlacements.ToolsMenu],
    };

    public override async Task ExecuteCommandAsync(IClientContext context, CancellationToken ct)
    {
        // Your logic here
    }
}

Key concepts

Concept	What it does
`[VisualStudioContribution]`	Registers a class as a VS contribution (command, tool window, etc.)
`CommandConfiguration`	Declares where a command appears, its icon, and visibility rules
`IClientContext`	Provides access to the current IDE state when a command executes
`Extensibility` property	Access to VS services (shell, editor, documents)
`Extension` class	The entry point that defines metadata for your extension

How it connects

Visual Studio                       Your Extension (separate process)
┌─────────────────────┐             ┌─────────────────────────────┐
│                     │  ← JSON →   │ ExtensionEntrypoint         │
│ Loads               │             │                             │
│ extension.json      │ ← Commands →│ MyCommand.ExecuteCommandAsync()│
│                     │             │                             │
│ Menu click ─────────│────────────>│                             │
│                     │             │                             │
│ Tool window <───────│─────────────│ RemoteUserControl           │
│                     │  ← UI →    │ (XAML + ViewModel)          │
└─────────────────────┘             └─────────────────────────────┘

Your extension runs in its own process. Visual Studio communicates with it via JSON-RPC. This isolates extension process crashes, though extension bugs can still affect the IDE.

Next steps

Add a command — the most common extension feature
Tool windows — add custom UI
Activation constraints — control when your extension is active
Dependency injection — how services are provided

Last updated on 2026-11-04