EF Core Add Migration Debugging

You should be able to call Debugger.Launch() in your code. The just-in-time debugger should prompt you to attach a debugger when it hits that line.

An alternate method would be to create your own console app or unit test and debug that. Use this snippet by bricelam from the ef github issue

using (var db = new MyDbContext())
{
    var reporter = new OperationReporter(
        new OperationReportHandler(
            m => Console.WriteLine("  error: " + m),
            m => Console.WriteLine("   warn: " + m),
            m => Console.WriteLine("   info: " + m),
            m => Console.WriteLine("verbose: " + m)));

    var designTimeServices = new ServiceCollection()
        .AddSingleton(db.GetService<IHistoryRepository>())
        .AddSingleton(db.GetService<IMigrationsIdGenerator>())
        .AddSingleton(db.GetService<IMigrationsModelDiffer>())
        .AddSingleton(db.GetService<IMigrationsAssembly>())
        .AddSingleton(db.Model)
        .AddSingleton(db.GetService<ICurrentDbContext>())
        .AddSingleton(db.GetService<IDatabaseProvider>())
        .AddSingleton<MigrationsCodeGeneratorDependencies>()
        .AddSingleton<ICSharpHelper, CSharpHelper>()
        .AddSingleton<CSharpMigrationOperationGeneratorDependencies>()
        .AddSingleton<ICSharpMigrationOperationGenerator, CSharpMigrationOperationGenerator>()
        .AddSingleton<CSharpSnapshotGeneratorDependencies>()
        .AddSingleton<ICSharpSnapshotGenerator, CSharpSnapshotGenerator>()
        .AddSingleton<CSharpMigrationsGeneratorDependencies>()
        .AddSingleton<IMigrationsCodeGenerator, CSharpMigrationsGenerator>()
        .AddSingleton<IOperationReporter>(reporter)
        .AddSingleton<MigrationsScaffolderDependencies>()
        .AddSingleton<MigrationsScaffolder>()
        .BuildServiceProvider();

    var scaffolder = designTimeServices.GetRequiredService<MigrationsScaffolder>();

    var migration = scaffolder.ScaffoldMigration(
        "MyMigration",
        "MyApp.Data");

    File.WriteAllText(
        migration.MigrationId + migration.FileExtension,
        migration.MigrationCode);
    File.WriteAllText(
        migration.MigrationId + ".Designer" + migration.FileExtension,
        migration.MetadataCode);
    File.WriteAllText(migration.SnapshotName + migration.FileExtension,
        migration.SnapshotCode);
}