diff --git a/GerbilManagerWebAPI/Endpoints/SaleAdEndpoints.cs b/GerbilManagerWebAPI/Endpoints/SaleAdEndpoints.cs
new file mode 100644
index 0000000..5f73ebc
--- /dev/null
+++ b/GerbilManagerWebAPI/Endpoints/SaleAdEndpoints.cs
@@ -0,0 +1,34 @@
+using GerbilManagerWebAPI.SaleAd;
+
+namespace GerbilManagerWebAPI.Endpoints
+{
+    /// <summary>
+    /// FEAT-12a: POST /gerbils/sale-ad — AI-gestütztes Abgabe-Inserat (frozen
+    /// contract, see gerbil-manager-web/src/api/saleAd.ts).
+    ///
+    /// 503 {code:"AiKeyMissing"} while the AI section is unconfigured — the
+    /// frontend maps exactly this code to its German disabled-state hint.
+    /// </summary>
+    public static class SaleAdEndpoints
+    {
+        public static IEndpointRouteBuilder MapSaleAdEndpoints(this IEndpointRouteBuilder app)
+        {
+            app.MapPost("/gerbils/sale-ad",
+                async (SaleAdRequest request, SaleAdService service, CancellationToken ct) =>
+                {
+                    var result = await service.GenerateAsync(request, ct);
+                    return result.Status switch
+                    {
+                        SaleAdStatus.Ok => Results.Ok(new SaleAdResponse(result.Text!)),
+                        SaleAdStatus.NotConfigured => Results.Json(
+                            new SaleAdError("AiKeyMissing", result.Error ?? ""), statusCode: 503),
+                        _ => Results.Json(
+                            new SaleAdError("AiUpstreamError", result.Error ?? ""), statusCode: 502),
+                    };
+                })
+                .WithTags("SaleAd");
+
+            return app;
+        }
+    }
+}
diff --git a/GerbilManagerWebAPI/Program.cs b/GerbilManagerWebAPI/Program.cs
index c4bfc3e..c960f6e 100644
--- a/GerbilManagerWebAPI/Program.cs
+++ b/GerbilManagerWebAPI/Program.cs
@@ -35,6 +35,13 @@ builder.Services.AddCors(options => options.AddPolicy(LanCorsPolicy, policy =>
 // OpenAPI document for the Scalar API reference (Swashbuckle removed).
 builder.Services.AddOpenApi();
 
+// FEAT-12a: provider-agnostic AI config (env vars AI__BaseUrl/AI__ApiKey/AI__Model
+// or user-secrets — never committed) + typed client for sale-ad generation.
+builder.Services.AddOptions<GerbilManagerWebAPI.SaleAd.AiOptions>()
+    .BindConfiguration(GerbilManagerWebAPI.SaleAd.AiOptions.SectionName);
+builder.Services.AddHttpClient<GerbilManagerWebAPI.SaleAd.SaleAdService>(
+    http => http.Timeout = TimeSpan.FromSeconds(60));
+
 var app = builder.Build();
 
 app.MapDefaultEndpoints();
@@ -62,5 +69,6 @@ app.MapHealthRecordEndpoints();
 app.MapWeightRecordEndpoints();
 app.MapInbreedingEndpoints();
 app.MapPhotoEndpoints();
+app.MapSaleAdEndpoints();
 
 app.Run();