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Setting up your C# (.NET) project for GitHub Codespaces

Get started with your C# (.NET) project in GitHub Codespaces by creating a custom dev container.

GitHub Codespaces は、GitHub Team または GitHub Enterprise Cloud を使用する Organization で利用できます。 GitHub Free および GitHub Pro プランの個人ユーザーも、GitHub Codespaces を制限付きのベータ リリースとして利用できます。 詳細については、「GitHub's products」を参照してください。


This guide shows you how to set up your C# (.NET) project in GitHub Codespaces. It will take you through an example of opening your project in a codespace, and adding and modifying a dev container configuration from a template.


  • You should have an existing C# (.NET) project in a repository on If you don't have a project, you can try this tutorial with the following example:
  • You must have GitHub Codespaces enabled for your organization.

Step 1: Open your project in a codespace

  1. Under the repository name, use the Code drop-down menu, and in the Codespaces tab, click Create codespace on main.

    New codespace button

    If you don’t see this option, GitHub Codespaces isn't available for your project. See Access to GitHub Codespaces for more information.

When you create a codespace, your project is created on a remote VM that is dedicated to you. By default, the container for your codespace has many languages and runtimes including .NET. It also includes a common set of tools like git, wget, rsync, openssh, and nano.

You can customize your codespace by adjusting the amount of vCPUs and RAM, adding dotfiles to personalize your environment, or by modifying the tools and scripts installed. For more information, see "Customizing your codespace."

GitHub Codespaces uses a file called devcontainer.json to configure the development container that you use when you work in a codespace. Each repository can contain one or more devcontainer.json files, to give you exactly the development environment you need to work on your code in a codespace.

On launch, GitHub Codespaces uses a devcontainer.json file, and any dependent files that make up the dev container configuration, to install tools and runtimes, and perform other setup tasks that the project requires. For more information, see "Introduction to dev containers."

Step 2: Add a dev container configuration to your repository from a template

The default development container, or "dev container," for GitHub Codespaces comes with the latest .NET version and common tools preinstalled. However, we recommend that you configure your own dev container to include all of the tools and scripts that your project needs. This will ensure a fully reproducible environment for all GitHub Codespaces users in your repository.

カスタム開発コンテナーを使用するようにリポジトリを設定するには、devcontainer.json ファイルを 1 つ以上作成する必要があります。 これらは、テンプレートからか Visual Studio Code 内に追加したり、独自のものを記述したりすることができます。 開発コンテナーの詳しい情報については、「開発コンテナーの概要」を参照してください。

  1. Visual Studio Code Command Palette にアクセスし (Shift + Command + P (Mac) / Ctrl + Shift + P (Windows/Linux))、「開発コンテナー」と入力します。 [コードスペース: 開発コンテナー構成ファイルの追加...] を選択します。

    Visual Studio Code Command Palette の「コードスペース: 開発コンテナー構成ファイルの追加...」

  2. For this example, click C# (.NET). If you need additional features you can select any container that’s specific to C# (.NET) or a combination of tools such as C# (.NET) and MS SQL. Select C# (.NET) option from the list

  3. Click the recommended version of .NET. .NET version selection

  4. Accept the default option to add Node.js to your customization. Add Node.js selection

  5. VS Code Command Palette にアクセスし (Shift + Command + P (Mac) / Ctrl + Shift + P (Windows/Linux))、「リビルド」と入力します。 [Codespaces: コンテナーのリビルド] を選択します。


Anatomy of your dev container

Adding the C# (.NET) dev container template adds a .devcontainer folder to the root of your project's repository with the following files:

  • devcontainer.json
  • Dockerfile

The newly added devcontainer.json file defines a few properties that are described after the sample.


	"name": "C# (.NET)",
	"build": {
		"dockerfile": "Dockerfile",
		"args": {
			// Update 'VARIANT' to pick a .NET Core version: 2.1, 3.1, 5.0
			"VARIANT": "5.0",
			// Options
			"INSTALL_NODE": "true",
			"NODE_VERSION": "lts/*",
			"INSTALL_AZURE_CLI": "false"

	// Set *default* container specific settings.json values on container create.
	"settings": {
		"": "/bin/bash"

	// Add the IDs of extensions you want installed when the container is created.
	"extensions": [

	// Use 'forwardPorts' to make a list of ports inside the container available locally.
	// "forwardPorts": [5000, 5001],

	// [Optional] To reuse of your local HTTPS dev cert:
	// 1. Export it locally using this command:
	//    * Windows PowerShell:
	//        dotnet dev-certs https --trust; dotnet dev-certs https -ep "$env:USERPROFILE/.aspnet/https/aspnetapp.pfx" -p "SecurePwdGoesHere"
	//    * macOS/Linux terminal:
	//        dotnet dev-certs https --trust; dotnet dev-certs https -ep "${HOME}/.aspnet/https/aspnetapp.pfx" -p "SecurePwdGoesHere"
	// 2. Uncomment these 'remoteEnv' lines:
	//    "remoteEnv": {
	// 	      "ASPNETCORE_Kestrel__Certificates__Default__Password": "SecurePwdGoesHere",
	//        "ASPNETCORE_Kestrel__Certificates__Default__Path": "/home/vscode/.aspnet/https/aspnetapp.pfx",
	//    },
	// 3. Do one of the following depending on your scenario:
	//    * When using GitHub Codespaces and/or Remote - Containers:
	//      1. Start the container
	//      2. Drag ~/.aspnet/https/aspnetapp.pfx into the root of the file explorer
	//      3. Open a terminal in VS Code and run "mkdir -p /home/vscode/.aspnet/https && mv aspnetapp.pfx /home/vscode/.aspnet/https"
	//    * If only using Remote - Containers with a local container, uncomment this line instead:
	//      "mounts": [ "source=${env:HOME}${env:USERPROFILE}/.aspnet/https,target=/home/vscode/.aspnet/https,type=bind" ],

	// Use 'postCreateCommand' to run commands after the container is created.
	// "postCreateCommand": "dotnet restore",

	// Comment out connect as root instead. More info:
	"remoteUser": "vscode"
  • name - You can name our dev container anything, this is just the default.
  • build - The build properties.
    • dockerfile - In the build object, dockerfile contains the path to the Dockerfile that was also added from the template.
    • args
      • variant: This file only contains one build argument, which is the .NET Core version that we want to use.
  • settings - These are Visual Studio Code settings.
    • - While bash is the default here, you could use other terminal shells by modifying this.
  • extensions - These are extensions included by default.
    • ms-dotnettools.csharp - The Microsoft C# extension provides rich support for developing in C#, including features such as IntelliSense, linting, debugging, code navigation, code formatting, refactoring, variable explorer, test explorer, and more.
  • forwardPorts - Any ports listed here will be forwarded automatically. For more information, see "Forwarding ports in your codespace."
  • postCreateCommand - Use this to run commands that aren't defined in the Dockerfile, after your codespace is created.
  • remoteUser - By default, you’re running as the vscode user, but you can optionally set this to root.


# [Choice] .NET version: 5.0, 3.1, 2.1

# [Option] Install Node.js
RUN if [ "${INSTALL_NODE}" = "true" ]; then su vscode -c "umask 0002 && . /usr/local/share/nvm/ && nvm install ${NODE_VERSION} 2>&1"; fi

# [Option] Install Azure CLI
COPY library-scripts/ /tmp/library-scripts/
RUN if [ "$INSTALL_AZURE_CLI" = "true" ]; then bash /tmp/library-scripts/; fi \
    && apt-get clean -y && rm -rf /var/lib/apt/lists/* /tmp/library-scripts

# [Optional] Uncomment this section to install additional OS packages.
# RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
#     && apt-get -y install --no-install-recommends <your-package-list-here>

# [Optional] Uncomment this line to install global node packages.
# RUN su vscode -c "source /usr/local/share/nvm/ && npm install -g <your-package-here>" 2>&1

You can use the Dockerfile to add additional container layers to specify OS packages, node versions, or global packages we want included in our container.

Step 3: Modify your devcontainer.json file

With your dev container configuration added and a basic understanding of what everything does, you can now make changes to customize your environment further. In this example, you'll add properties to install extensions and your project dependencies when your codespace launches.

  1. In the Explorer, select the devcontainer.json file from the tree to open it. You might have to expand the .devcontainer folder to see it.

    devcontainer.json file in the Explorer

  2. Update your the extensions list in your devcontainer.json file to add a few extensions that are useful when working with your project.

    "extensions": [
  3. Uncomment the postCreateCommand to restore dependencies as part of the codespace setup process.

    // Use 'postCreateCommand' to run commands after the container is created.
    "postCreateCommand": "dotnet restore",

    For information about the settings and properties that you can set in a devcontainer.json file, see the Specification on the Development Containers website.

  4. VS Code Command Palette にアクセスし (Shift + Command + P (Mac) / Ctrl + Shift + P (Windows/Linux))、「リビルド」と入力します。 [Codespaces: コンテナーのリビルド] を選択します。


    リポジトリに変更をコミットする前に、codespace 内でリビルドすることにより期待どおりに変更が動作します。 何らかの失敗があった場合、コンテナの調整を継続するためにリビルドできるリカバリコンテナを備えた codespace に配置されます。

  5. Check your changes were successfully applied by verifying the "Code Spell Checker" extension was installed.

    Extensions list

Step 4: Run your application

In the previous section, you used the postCreateCommand to install a set of packages via the dotnet restore command. With our dependencies now installed, we can run our application.

  1. Run your application by pressing F5 or entering dotnet watch run in your terminal.

  2. When your project starts, you should see a toast in the bottom right corner with a prompt to connect to the port your project uses.

    Port forwarding toast

Step 5: Commit your changes

新しいコードであれ、設定の変更であれ、codespaceに変更を加えたら、その変更をコミットしたくなるでしょう。 リポジトリに変更をコミットすれば、このリポジトリからcodespaceを作成する他の人が、同じ設定になることを保証できます。 これはまた、VS Code 拡張機能の追加など、行うすべてのカスタマイズが、すべてのユーザーに対して現れるようになるということでもあります。


Next steps

You should now be ready start developing your C# (.NET) project in GitHub Codespaces. Here are some additional resources for more advanced scenarios.