What is GitHub Copilot app modernization - upgrade for .NET?

2025-06-06

GitHub Copilot app modernization - upgrade for .NET is a powerful Visual Studio extension that works with you to upgrade projects to newer versions of .NET, upgrade your dependencies, and apply code fixes.

GitHub Copilot app modernization is distributed as a Visual Studio extension, and is an interactive upgrade process.

Prerequisites

Windows Operating System
Visual Studio 2022 version 17.14 or newer.
.NET desktop development workload.
Sign in to Visual Studio using a GitHub account with Copilot access.

Supported subscription plans:
- Copilot Pro
- Copilot Pro+
- Copilot Business
- Copilot Enterprise

(If you change subscriptions, you must restart Visual Studio.)

Code must be in a local Git repository.
Code must be written in C#.
Optional but recommended: Use GitHub Copilot agent mode for the upgrade process. For more information, see Use Copilot agent mode in Visual Studio.

For installation instructions, see Install GitHub Copilot app modernization - upgrade for .NET.

Supported project types

GitHub Copilot app modernization supports upgrading projects coded in C#. The following types of projects are supported:

ASP.NET and related technologies such as MVC, Razor Pages, Web API
Blazor
Azure Functions
Windows Presentation Foundation
Windows Forms
Class libraries
Console apps

Important

The current version of the extension doesn't support upgrading from .NET Framework to .NET. In these scenarios, use the .NET Upgrade Assistant to migrate to .NET, then use this tool to modernize your code.

Upgrade paths

The following upgrade paths are supported:

Upgrade projects from .NET Core to .NET.
Upgrade projects from older versions of .NET to the latest.
Modernize your code base.

Start the upgrade process

The first step to upgrading is generating a plan by interacting with GitHub Copilot. There are two ways to get Copilot to use the tool:

Right-click on the solution or project and select Upgrade with GitHub Copilot.

—or—
Enable GitHub Copilot agent mode, and ask a new Copilot chat to upgrade the solution or project.

Important

After enabling GitHub Copilot agent mode, set the chat mode to Agent and enable the upgrade_start tool.

Generate a plan

Once the process starts, Copilot analyzes your projects and their dependencies, and then asks you a series of questions about the upgrade. After you answer these questions, an upgrade plan is written in the form of a Markdown file. If you tell Copilot to proceed with the upgrade, this plan describes the steps of the upgrade process.

You can adjust the plan by editing the Markdown file to change the upgrade steps or add more context.

Caution

The plan is generated based on the inter-dependencies of your projects. The upgrade won't succeed if you modify the plan in such a way that the migration path can't complete. For example, if Project A depends on Project B and you remove Project B from the upgrade plan, upgrading Project A might fail.

The following snippet demonstrates the structure of a plan:

# .NET 9.0 Upgrade Plan

## Execution Steps

1. Validate that an .NET 9.0 SDK required for this upgrade is installed on the machine and if not, help to get it installed.
2. Ensure that the SDK version specified in global.json files is compatible with the .NET 9.0 upgrade.
3. Upgrade projects to .NET 9.0.
  - 3.1. Upgrade RazorMovie.csproj
  - 3.2. Upgrade RazorMovie.Tests.csproj
4. Run unit tests to validate upgrade in the projects listed below:
  - RazorMovie.Tests.csproj

## Settings

This section contains settings and data used by execution steps.

### Aggregate NuGet packages modifications across all projects

NuGet packages used across all selected projects or their dependencies that need version update in projects that reference them.

| Package Name                                     | Current Version     | New Version | Description              |
|:-------------------------------------------------|:-------------------:|:-----------:|:-------------------------|
| HtmlSanitizer                                    | 7.1.542             | 9.0.884     | Security vulnerability   |
| Microsoft.Data.SqlClient                         | 4.0.5               | 6.0.2       | Deprecated               |
| Microsoft.EntityFrameworkCore.Design             | 6.0.0-rtm.21467.1   | 9.0.5       | Recommended for .NET 9.0 |
| Microsoft.EntityFrameworkCore.SqlServer          | 6.0.0-rc.1.21452.10 | 9.0.5       | Recommended for .NET 9.0 |
| Microsoft.EntityFrameworkCore.Tools              | 6.0.0-rc.1.21452.10 | 9.0.5       | Recommended for .NET 9.0 |
| Microsoft.VisualStudio.Web.CodeGeneration.Design | 6.0.0-rc.1.21464.1  | 9.0.0       | Recommended for .NET 9.0 |

...

Perform the upgrade

Once an upgrade plan is ready, tell Copilot to start the upgrade. Once the upgrade process starts, Copilot lets you know what it's doing in the chat window and it opens the Upgrade Progress Details document, which lists the status of every step. If it runs into a problem, Copilot pauses and asks for your direction or help in fixing these problems.

The tool differs in experience based on whether or not Copilot agent mode is enabled.

Copilot agent mode

When Copilot agent mode is enabled and used, Copilot tries to identify the cause of a problem and apply a fix. If Copilot can't seem to correct the problem, it asks for your help. When you intervene, Copilot learns from the changes you make and tries to automatically apply them for you, if the problem is encountered again.
Copilot fix mode

Copilot fix mode is used if agent mode is disabled or not used. Copilot reports the problems it finds and guides you through the fixes required. It relies on you to perform the actual code changes and then it verifies those fixes.

Each major step in the upgrade process is committed to the local Git repository.

Upgrade results

When the upgrade completes, a report is generated that describes every step of the upgrade. The tool creates a Git commit for every portion of the upgrade process, so you can easily roll back the changes or get detailed information about what changed. The report contains the Git commit hashes.

The report also provides a Next steps section that describes the steps you should take after the upgrade finishes. The following example shows the report of a completed upgrade that contained a test failure:

# .NET 9 Upgrade Report

## Project modifications

| Project name                                   | Old Target Framework    | New Target Framework         | Commits                   |
|:-----------------------------------------------|:-----------------------:|:----------------------------:|---------------------------|
| RazorMovie                                     |   net6.0                | net9.0                       | af8cf633, aa61a18d        |
| MvcMovie                                       |   net6.0                | net9.0                       | cc8c9015                  |
| WpfMovie                                       |   net6.0-windows        | net9.0-windows               | 9c4b13f9                  |
| RazorMovie.Tests                               |   net6.0                | net9.0                       | b8d85e97                  |
| MvcMovie.Tests                                 |   net6.0                | net9.0                       | b8d85e97                  |
| WpfMovie.Tests                                 |   net6.0-windows        | net9.0-windows7.0            | b8d85e97                  |

## NuGet Packages

| Package Name                                     | Old Version         | New Version | Commit Id |
|:-------------------------------------------------|:-------------------:|:-----------:|-----------|
| HtmlSanitizer                                    | 7.1.542             | 9.0.884     | af8cf633  |
| Microsoft.Data.SqlClient                         | 4.0.5               | 6.0.2       | bf8deeac  |
| Microsoft.EntityFrameworkCore.Design             | 6.0.0-rtm.21467.1   | 9.0.5       | bf8deeac  |
| Microsoft.EntityFrameworkCore.SqlServer          | 6.0.0-rc.1.21452.10 | 9.0.5       | bf8deeac  |
| Microsoft.EntityFrameworkCore.Tools              | 6.0.0-rc.1.21452.10 | 9.0.5       | bf8deeac  |
| Microsoft.VisualStudio.Web.CodeGeneration.Design | 6.0.0-rc.1.21464.1  | 9.0.0       | bf8deeac  |

## All commits

| Commit ID | Description                                             |
|:----------|:--------------------------------------------------------|
| af8cf633  | Update HtmlSanitizer package in RazorMovie.csproj       |
| aa61a18d  | Upgrade target framework in RazorMovie.csproj           |
| cc8c9015  | Upgrade to .NET 9 and update dependencies               |
| bf8deeac  | Update package references in MvcMovie.csproj            |
| 9c4b13f9  | Update WpfMovie.csproj to target .NET 9.0               |
| b8d85e97  | Update test projects to .NET 9 and enhance dependencies |

## Test Results

| Project Name           | Passed | Failed | Skipped |
|:-----------------------|:------:|:------:|:-------:|
| RazorMovie.Tests       |   0    |   0    |    0    |
| MvcMovie.Tests         |   2    |   0    |    0    |
| WpfMovie.Tests         |   6    |   1    |    0    |

## Next steps

- Review the test results and address the single failing test in `WpfMovie.Tests`.
- Ensure all updated NuGet packages are compatible with your application.
- Leverage new features and improvements in .NET 9.0 for your projects.

Telemetry

The tool only collects data about project types, intent to upgrade, and upgrade duration. The data is collected and aggregated through Visual Studio itself and doesn't contain any user-identifiable information. For more information about Microsoft's privacy policy, see Visual Studio Customer Experience Improvement Program.

Share via