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How to set up and use C# LSTs with the Moderne CLI

Moderne supports C# LSTs, enabling semantically-aware refactoring of C# code. With C# LSTs, recipes can resolve types, understand project references, and make precise automated changes across your .NET repositories.

In this guide, we'll walk you through how to configure the Moderne CLI to take advantage of C# support.

Prerequisites​

This guide assumes that:

info

The C# recipe runtime (rewrite-csharp) is packaged as a net10.0 application, so the .NET 10 runtime is required. Earlier SDK versions (8.0, 9.0) will not work.

Step 1: Update your moderne.yml file​

In order to enable C# support, you will need to update the build steps in your moderne.yml file to include .NET. This file is located at ~/.moderne/cli/moderne.yml and is created when you first set up the CLI.

If your moderne.yml file already includes a build section, you can just add the - type: dotnet line to the end of your build steps. If it doesn't, you will need to add the entire section as seen in the example below:

moderne.yml
# Other keys and values...
license:
  key: some-license
tenant:
  host: https://app.moderne.io
  apiHost: https://api.app.moderne.io
  skipSsl: false
  authorization: Bearer mat-some-token
build:
  steps:
    - type: maven
    - type: gradle
    - type: bazel
    - type: dotnet
    - type: resource
      inclusion: |-
        **/*

Step 2: (Optionally) Configure your .NET installation​

By default, the CLI automatically detects .NET SDK installations in standard locations on your machine.

Discovering installations​

You can see all detected .NET installations by running:

mod config dotnet installation list

Adding installation locations​

If .NET is installed in a non-standard location (for example, at ~/.dotnet via the official dotnet-install script), you can register it:

mod config dotnet installation edit /path/to/dotnet-root

Each path should point to a .NET installation root directory (i.e., a directory containing the dotnet executable).

To remove manually configured installation paths:

mod config dotnet installation delete

Setting DOTNET_ROOT for non-standard installs​

Even with an installation registered, the C# recipe subprocess relies on the DOTNET_ROOT environment variable and PATH to locate the runtime. If your .NET SDK is not in a system-wide path, you will need to export both before running mod commands:

export PATH="$HOME/.dotnet:$PATH"
export DOTNET_ROOT="$HOME/.dotnet"
tip

Without these environment variables, mod config recipes nuget install and mod run can fail with You must install .NET to run this application — even when mod config dotnet installation list shows a valid path.

Adjusting the build timeout​

.NET project parsing can take longer than other ecosystems on large solutions. To override the default build timeout:

mod config build dotnet timeout edit <DURATION>

Use an ISO-8601 duration (for example, PT30M for 30 minutes). To see the currently configured timeout:

mod config build dotnet timeout show

To revert to the default:

mod config build dotnet timeout delete

Step 3: (Optionally) Clone a custom list of repositories​

If you don't have the repositories you want to work with cloned locally already, you can clone a group of them by defining a repos.csv file that lists them out such as in the following example:

repos.csv
cloneUrl,branch,origin,path
git@github.com:dotnetcore/DotnetSpider.git,master,github.com,dotnetcore/DotnetSpider
git@github.com:GitTools/GitVersion.git,main,github.com,GitTools/GitVersion
git@github.com:MessagePack-CSharp/MessagePack-CSharp.git,master,github.com,MessagePack-CSharp/MessagePack-CSharp
git@github.com:Azure/DotNetty.git,dev,github.com,Azure/DotNetty
git@github.com:chocolatey/choco.git,develop,github.com,chocolatey/choco
tip

Check out our documentation on creating a repos.csv file for more detailed information about what's expected in this file.

After creating the CSV, clone the repositories by running the following command:

mod git sync csv . repos.csv --with-sources

Step 4: Build your C# repositories​

The next thing you'll need to do is build LSTs for each of your repositories. To build the LSTs, run:

mod build /path/to/your/repos

Presuming everything has been set up correctly, you should see output similar to:

▶ dotnetcore/DotnetSpider@master
    Build output will be written to build.log
    > Step 1 - build with .NET
        Selected .NET 10.0.7
        Processing .NET project: .
    Running dotnet restore
        Parsing DotnetSpider.sln
        Starting C# solution parsing: /Users/someuser/repos/dotnetcore/DotnetSpider/DotnetSpider.sln
        Discovered 263 files to parse
    ✓ Built DotnetSpider-20260424080833161-ast.jar
    Cleaned 2 older builds

Step 5: Install recipes​

In order to run recipes, you'll need to make sure the recipes are installed on your local machine.

You can install a specific C# recipe package from NuGet by running a command like:

mod config recipes nuget install OpenRewrite.MigrateDotNet
tip

You can find the specific installation command for any recipe on its page in the recipe catalog.

Step 6: Run recipes​

With the LSTs built and recipes installed, you can now run recipes against your C# repositories. You can either specify the full recipe path for running such as in:

mod run . --recipe=OpenRewrite.Recipes.Net10.UpgradeToDotNet10

Or, you can search for a specific recipe and set it as the active recipe:

mod config recipes search UpgradeToDotNet10

Then you can run the active recipe by:

mod run . --active-recipe

Step 7: View data tables​

Many recipes will also produce useful data tables that you can access via the mod study command such as in:

mod study . --last-recipe-run --data-table SourcesFileResults

Moderne CLI 4.1.9

⏺ Reading organization

Found 1 organization containing 1 repository (1s)
Found recipe run 20260424080921-OKpr8

⏺ Building CSV output for each organization

▶ C# Demos
    ✓ Data table produced
Done (1s)

⏺ Converting to Excel for each organization

▶ C# Demos
    ✓ Added 4 rows
    ✓ Data table produced
Done (1s)

Data tables for each organization with rows are linked above