diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/service/AiRequestComposer.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/service/AiRequestComposer.java
index 0a2ce6c..edf11fa 100644
--- a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/service/AiRequestComposer.java
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/service/AiRequestComposer.java
@@ -15,16 +15,25 @@ import de.gecheckt.pdf.umbenenner.domain.model.PromptIdentifier;
  *   <li>The loaded prompt content (from the external prompt file)</li>
  *   <li>The stable prompt identifier (derived from the prompt source)</li>
  *   <li>The extracted document text (already limited to max characters if needed)</li>
+ *   <li>An explicit JSON-only response format specification</li>
  *   <li>The exact character count that was sent (for traceability)</li>
  * </ul>
  * <p>
- * <strong>Order and structure:</strong> The composition follows a fixed, documented order
- * to ensure that another implementation would not need to guess how the prompt and document
- * are combined. The prompt is presented first, followed by the document text, with clear
- * structural markers to distinguish between them.
+ * <strong>Composition order:</strong> The request follows a fixed, documented order:
+ * <ol>
+ *   <li>Prompt content (instruction)</li>
+ *   <li>Prompt identifier marker</li>
+ *   <li>Document text marker</li>
+ *   <li>Document text content</li>
+ *   <li>Response format expectation (JSON-only specification)</li>
+ * </ol>
  * <p>
- * <strong>JSON-only response expectation:</strong> The request is constructed with the
- * explicit expectation that the AI will respond with a JSON object containing:
+ * This fixed order ensures reproducibility and allows another implementation to
+ * understand the request structure without guessing.
+ * <p>
+ * <strong>JSON-only response expectation:</strong> The actual composed request includes
+ * an explicit specification that the AI must respond with a JSON object containing
+ * exactly these fields:
  * <ul>
  *   <li>{@code title} — mandatory, max 20 characters (base title)</li>
  *   <li>{@code reasoning} — mandatory, the AI's explanation</li>
@@ -38,22 +47,27 @@ public class AiRequestComposer {
     /**
      * Composes a deterministic AI request representation.
      * <p>
-     * The composition order is fixed:
+     * The composition order is fixed and documented to ensure determinism and
+     * to make the structure obvious to any reader:
      * <ol>
-     *   <li>Prompt content</li>
-     *   <li>Separator: newline</li>
-     *   <li>Prompt identifier (for reference/traceability)</li>
-     *   <li>Separator: newline</li>
+     *   <li>Prompt content (instruction)</li>
+     *   <li>Newline separator</li>
+     *   <li>Prompt identifier marker (e.g., "--- Prompt-ID: filename ---")</li>
+     *   <li>Newline separator</li>
      *   <li>Document text section marker</li>
+     *   <li>Newline separator</li>
      *   <li>Document text content</li>
+     *   <li>Newline separator</li>
+     *   <li>Response format specification (JSON-only with required fields)</li>
      * </ol>
      * <p>
      * This fixed order ensures that:
      * <ul>
      *   <li>The prompt guides the AI</li>
      *   <li>The document text is clearly separated and identified</li>
-     *   <li>Another implementation knows exactly where each part begins</li>
-     *   <li>The composition is deterministic and reproducible</li>
+     *   <li>The response format expectation is explicit in the actual request</li>
+     *   <li>Another implementation knows exactly where each part begins and ends</li>
+     *   <li>The composition is deterministic and reproducible across runs</li>
      * </ul>
      *
      * @param promptIdentifier the stable identifier for this prompt; must not be null
@@ -71,17 +85,19 @@ public class AiRequestComposer {
         Objects.requireNonNull(promptContent, "promptContent must not be null");
         Objects.requireNonNull(documentText, "documentText must not be null");
 
-        // The complete request text is composed in a deterministic order:
+        // The complete request text is composed in a fixed, deterministic order:
         // 1. Prompt content (instruction)
         // 2. Newline separator
-        // 3. Prompt identifier (for reference)
+        // 3. Prompt identifier marker (for traceability)
         // 4. Newline separator
         // 5. Document text section marker
         // 6. Newline separator
         // 7. Document text content
+        // 8. Newline separator
+        // 9. Response format specification (JSON-only with required fields)
         //
         // This order is fixed so that another implementation knows exactly where
-        // the prompt and document text are positioned.
+        // each part is positioned and what to expect.
         StringBuilder requestBuilder = new StringBuilder();
         requestBuilder.append(promptContent);
         requestBuilder.append("\n");
@@ -90,6 +106,8 @@ public class AiRequestComposer {
         requestBuilder.append("--- Document Text ---");
         requestBuilder.append("\n");
         requestBuilder.append(documentText);
+        requestBuilder.append("\n");
+        appendJsonResponseFormat(requestBuilder);
 
         // Record the exact character count of the document text that was included.
         // This is the length of the document text (not the complete request).
@@ -107,12 +125,13 @@ public class AiRequestComposer {
      * <p>
      * This is a helper method that builds the exact string that would be included in the
      * HTTP request to the AI service. It follows the same deterministic order as
-     * {@link #compose(PromptIdentifier, String, String)}.
+     * {@link #compose(PromptIdentifier, String, String)}, including the explicit
+     * JSON-only response format specification.
      *
      * @param promptIdentifier the stable identifier for this prompt; must not be null
      * @param promptContent the prompt template content; must not be null
      * @param documentText the extracted document text; must not be null
-     * @return the complete, deterministically-ordered request text for the AI
+     * @return the complete, deterministically-ordered request text for the AI (includes JSON format spec)
      * @throws NullPointerException if any parameter is null
      */
     public static String buildCompleteRequestText(
@@ -132,10 +151,37 @@ public class AiRequestComposer {
         requestBuilder.append("--- Document Text ---");
         requestBuilder.append("\n");
         requestBuilder.append(documentText);
+        requestBuilder.append("\n");
+        appendJsonResponseFormat(requestBuilder);
 
         return requestBuilder.toString();
     }
 
+    /**
+     * Appends the explicit JSON-only response format specification to the request.
+     * <p>
+     * This ensures that the AI knows it must respond with a JSON object containing
+     * exactly these fields: {@code title}, {@code reasoning}, and optionally {@code date}.
+     * <p>
+     * This specification is part of the deterministic composition and is included in
+     * the actual request text sent to the AI service.
+     *
+     * @param requestBuilder the StringBuilder to append the format specification to
+     */
+    private static void appendJsonResponseFormat(StringBuilder requestBuilder) {
+        requestBuilder.append("--- Response Format (JSON-only) ---");
+        requestBuilder.append("\n");
+        requestBuilder.append("Respond with a JSON object containing exactly:");
+        requestBuilder.append("\n");
+        requestBuilder.append("  \"title\": string (mandatory, max 20 characters, base title only)");
+        requestBuilder.append("\n");
+        requestBuilder.append("  \"reasoning\": string (mandatory, explanation of the decision)");
+        requestBuilder.append("\n");
+        requestBuilder.append("  \"date\": string (optional, YYYY-MM-DD format if provided)");
+        requestBuilder.append("\n");
+        requestBuilder.append("No text outside the JSON object.");
+    }
+
     private AiRequestComposer() {
         // Static utility class – no instances
     }
diff --git a/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/service/AiRequestComposerTest.java b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/service/AiRequestComposerTest.java
index 5279378..cdcbe89 100644
--- a/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/service/AiRequestComposerTest.java
+++ b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/service/AiRequestComposerTest.java
@@ -192,4 +192,70 @@ class AiRequestComposerTest {
         assertThat(result).contains("Prompt\nwith\nnewlines");
         assertThat(result).contains("Document\ntext");
     }
+
+    @Test
+    void buildCompleteRequestText_shouldIncludeJsonResponseFormat() {
+        // Given
+        PromptIdentifier promptId = new PromptIdentifier("prompt.txt");
+        String promptContent = "Analyze the document.";
+        String documentText = "Sample document content";
+
+        // When
+        String result = AiRequestComposer.buildCompleteRequestText(promptId, promptContent, documentText);
+
+        // Then
+        // Verify that the actual composed request includes JSON response format specification
+        assertThat(result).contains("Response Format (JSON-only)");
+        assertThat(result).contains("\"title\"");
+        assertThat(result).contains("\"reasoning\"");
+        assertThat(result).contains("\"date\"");
+        assertThat(result).contains("mandatory");
+        assertThat(result).contains("optional");
+        assertThat(result).contains("No text outside the JSON object");
+    }
+
+    @Test
+    void buildCompleteRequestText_shouldHaveDeterministicJsonFormatOrder() {
+        // Given
+        PromptIdentifier promptId = new PromptIdentifier("prompt.txt");
+        String promptContent = "Process this.";
+        String documentText = "Document to process";
+
+        // When
+        String result = AiRequestComposer.buildCompleteRequestText(promptId, promptContent, documentText);
+
+        // Then
+        // Verify deterministic order: document text comes before JSON response format
+        int documentTextIndex = result.indexOf(documentText);
+        int jsonFormatIndex = result.indexOf("Response Format (JSON-only)");
+        assertThat(documentTextIndex).isLessThan(jsonFormatIndex);
+
+        // Verify JSON field order: title before reasoning, reasoning before date
+        int titleIndex = result.indexOf("\"title\"");
+        int reasoningIndex = result.indexOf("\"reasoning\"");
+        int dateIndex = result.indexOf("\"date\"");
+        assertThat(titleIndex).isLessThan(reasoningIndex);
+        assertThat(reasoningIndex).isLessThan(dateIndex);
+    }
+
+    @Test
+    void buildCompleteRequestText_shouldProduceCompleteRequest_withAllSections() {
+        // Given
+        PromptIdentifier promptId = new PromptIdentifier("prompt_v3.txt");
+        String promptContent = "Classify the document.";
+        String documentText = "Content to classify";
+
+        // When
+        String result = AiRequestComposer.buildCompleteRequestText(promptId, promptContent, documentText);
+
+        // Then
+        // Verify all sections are present in the actual composed request
+        assertThat(result)
+            .contains("Classify the document.") // prompt
+            .contains("--- Prompt-ID: prompt_v3.txt ---") // identifier
+            .contains("--- Document Text ---") // document marker
+            .contains("Content to classify") // document text
+            .contains("--- Response Format (JSON-only) ---") // JSON format marker
+            .contains("Respond with a JSON object containing exactly:"); // JSON instruction
+    }
 }