diff --git a/fundamentals/aot/diagnostics/Rdg12/Program.cs b/fundamentals/aot/diagnostics/Rdg12/Program.cs
new file mode 100644
index 0000000..de094fa
--- /dev/null
+++ b/fundamentals/aot/diagnostics/Rdg12/Program.cs
@@ -0,0 +1,59 @@
+#define RDG12F //   RDG12 RDG12F
+#if NEVER
+#elif RDG12
+// <snippet_1>
+var builder = WebApplication.CreateSlimBuilder(args);
+
+var app = builder.Build();
+app.MapEndpoints();
+app.Run();
+
+public static class TodoRouteBuilderExtensions
+{
+    public static IEndpointRouteBuilder MapEndpoints(this IEndpointRouteBuilder app)
+    {
+        app.MapPost("/input", (Todo value) => value);
+        app.MapGet("/result", () => new Todo());
+        app.MapPost("/input-with-wrapper", (Wrapper<Todo> value) => value);
+        app.MapGet("/async", async () =>
+        {
+            await Task.CompletedTask;
+            return new Todo();
+        });
+        return app;
+    }
+
+    private record Todo { };
+}
+
+record Wrapper<T> { }
+// </snippet_1>
+#elif RDG12F
+// <snippet_1f>
+var builder = WebApplication.CreateSlimBuilder(args);
+
+var app = builder.Build();
+app.MapEndpoints();
+app.Run();
+
+public static class TodoRouteBuilderExtensions
+{
+    public static IEndpointRouteBuilder MapEndpoints(this IEndpointRouteBuilder app)
+    {
+        app.MapPost("/input", (Todo value) => value);
+        app.MapGet("/result", () => new Todo());
+        app.MapPost("/input-with-wrapper", (Wrapper<Todo> value) => value);
+        app.MapGet("/async", async () =>
+        {
+            await Task.CompletedTask;
+            return new Todo();
+        });
+        return app;
+    }
+
+    public record Todo { };
+}
+
+record Wrapper<T> { }
+// </snippet_1f>
+#endif
diff --git a/fundamentals/aot/diagnostics/Rdg12/Rdg12.csproj b/fundamentals/aot/diagnostics/Rdg12/Rdg12.csproj
new file mode 100644
index 0000000..c12d03b
--- /dev/null
+++ b/fundamentals/aot/diagnostics/Rdg12/Rdg12.csproj
@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <EnableRequestDelegateGenerator>true</EnableRequestDelegateGenerator>
+    <LangVersion>preview</LangVersion>
+  </PropertyGroup>
+
+</Project>
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