diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f89d566..543d8de 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -52,6 +52,35 @@ jobs:
       - name: Test and package
         run: ./mvnw --batch-mode --no-transfer-progress verify
 
+      - name: Validate API proof asset
+        run: |
+          test -s docs/library-api-error-proof.jpg
+          python3 - <<'PY'
+          from pathlib import Path
+
+          proof = Path("docs/library-api-error-proof.jpg").read_bytes()
+          assert proof[:2] == b"\xff\xd8", "proof asset is not a JPEG"
+
+          offset = 2
+          dimensions = None
+          start_of_frame = {0xC0, 0xC1, 0xC2, 0xC3, 0xC5, 0xC6, 0xC7, 0xC9, 0xCA, 0xCB, 0xCD, 0xCE, 0xCF}
+          while offset < len(proof):
+              assert proof[offset] == 0xFF, "invalid JPEG marker"
+              marker = proof[offset + 1]
+              offset += 2
+              if marker in {0xD8, 0xD9}:
+                  continue
+              length = int.from_bytes(proof[offset:offset + 2], "big")
+              if marker in start_of_frame:
+                  height = int.from_bytes(proof[offset + 3:offset + 5], "big")
+                  width = int.from_bytes(proof[offset + 5:offset + 7], "big")
+                  dimensions = (width, height)
+                  break
+              offset += length
+
+          assert dimensions == (1280, 720), "proof asset must be 1280x720"
+          PY
+
       - name: Validate Compose contract
         run: docker compose --env-file .env.example config --quiet
 
diff --git a/README.md b/README.md
index af59cd0..30699a1 100644
--- a/README.md
+++ b/README.md
@@ -13,6 +13,12 @@ Kütüphaneler tarafından kullanılabilecek kayıt yönetimlerini, kitap ödün
 - Java 17'ye sabitlenmiş container build/runtime aşamaları ve PostgreSQL servis sağlık kontrolü.
 - Kaynakta parola tutmayan Compose yapılandırması ve Java 17/PostgreSQL CI doğrulaması.
 
+## Canlı API Kanıtı
+
+![Swagger UI'da var olmayan kategori isteğinin global hata yönetimiyle 404 dönmesi](docs/library-api-error-proof.jpg)
+
+*Gerçek Java 17/PostgreSQL 16 container çalıştırmasından alınmıştır. Swagger UI, `DataLoader` tarafından üretilen sentetik yerel veriler üzerinde `GET /api/v1/categories/999999` isteğini çalıştırır; fork'ta eklenen global hata yönetimi de tam 404 yanıtını üretir. Bu, barındırılan bir demo değil, yerel ve tekrar üretilebilir bir çalışma kanıtıdır.*
+
 ## Kullanılan Teknolojiler
 
 <code><img width="50" src="https://user-images.githubusercontent.com/25181517/117201156-9a724800-adec-11eb-9a9d-3cd0f67da4bc.png" alt="Java" title="Java"/></code>
diff --git a/docs/library-api-error-proof.jpg b/docs/library-api-error-proof.jpg
new file mode 100644
index 0000000..ea1e6b1
Binary files /dev/null and b/docs/library-api-error-proof.jpg differ
diff --git a/src/test/java/com/alisimsek/LibraryManagementProject/CategoryErrorResponseIntegrationTests.java b/src/test/java/com/alisimsek/LibraryManagementProject/CategoryErrorResponseIntegrationTests.java
new file mode 100644
index 0000000..f92fe36
--- /dev/null
+++ b/src/test/java/com/alisimsek/LibraryManagementProject/CategoryErrorResponseIntegrationTests.java
@@ -0,0 +1,26 @@
+package com.alisimsek.LibraryManagementProject;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.web.servlet.MockMvc;
+
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+@SpringBootTest
+@AutoConfigureMockMvc
+class CategoryErrorResponseIntegrationTests {
+
+    @Autowired
+    private MockMvc mockMvc;
+
+    @Test
+    void missingCategoryUsesTheForksGlobalErrorResponse() throws Exception {
+        mockMvc.perform(get("/api/v1/categories/{id}", 999999L))
+                .andExpect(status().isNotFound())
+                .andExpect(content().string("Category with ID 999999 not found in the system."));
+    }
+}