diff --git a/packages/genui/lib/src/facade/prompt_builder.dart b/packages/genui/lib/src/facade/prompt_builder.dart
index 3a0e1c5ae..77ecada7c 100644
--- a/packages/genui/lib/src/facade/prompt_builder.dart
+++ b/packages/genui/lib/src/facade/prompt_builder.dart
@@ -311,7 +311,7 @@ To update an existing UI:
       _fenced('''
 When constructing UI, you must output a VALID A2UI JSON object representing one of the A2UI message types ($_operationsFormatted).
 - You can treat the A2UI schema as a specification for the JSON you typically output.
-- You may include a brief conversational explanation before or after the JSON block if it helps the user, but the JSON block must be valid and complete.
+- The JSON block must be valid and complete.
 - Ensure your JSON is fenced with ```json and ```.
 ''', sectionName: 'OUTPUT FORMAT'),
     );
diff --git a/packages/genui/test/facade/prompt_builder_test.golden/all_operations_with_dataModel_false.txt b/packages/genui/test/facade/prompt_builder_test.golden/all_operations_with_dataModel_false.txt
index 6c6165e4d..2d5ebf136 100644
--- a/packages/genui/test/facade/prompt_builder_test.golden/all_operations_with_dataModel_false.txt
+++ b/packages/genui/test/facade/prompt_builder_test.golden/all_operations_with_dataModel_false.txt
@@ -119,7 +119,7 @@ To update an existing UI:
 -----OUTPUT_FORMAT_START-----
 When constructing UI, you must output a VALID A2UI JSON object representing one of the A2UI message types (`createSurface`, `updateComponents`, `deleteSurface`).
 - You can treat the A2UI schema as a specification for the JSON you typically output.
-- You may include a brief conversational explanation before or after the JSON block if it helps the user, but the JSON block must be valid and complete.
+- The JSON block must be valid and complete.
 - Ensure your JSON is fenced with ```json and ```.
 -----OUTPUT_FORMAT_END-----
 
diff --git a/packages/genui/test/facade/prompt_builder_test.golden/all_operations_with_dataModel_true.txt b/packages/genui/test/facade/prompt_builder_test.golden/all_operations_with_dataModel_true.txt
index 92e1acb59..ab826bcd9 100644
--- a/packages/genui/test/facade/prompt_builder_test.golden/all_operations_with_dataModel_true.txt
+++ b/packages/genui/test/facade/prompt_builder_test.golden/all_operations_with_dataModel_true.txt
@@ -121,7 +121,7 @@ To update an existing UI:
 -----OUTPUT_FORMAT_START-----
 When constructing UI, you must output a VALID A2UI JSON object representing one of the A2UI message types (`createSurface`, `updateComponents`, `deleteSurface`, `updateDataModel`).
 - You can treat the A2UI schema as a specification for the JSON you typically output.
-- You may include a brief conversational explanation before or after the JSON block if it helps the user, but the JSON block must be valid and complete.
+- The JSON block must be valid and complete.
 - Ensure your JSON is fenced with ```json and ```.
 -----OUTPUT_FORMAT_END-----
 
diff --git a/packages/genui/test/facade/prompt_builder_test.golden/create_and_update_with_dataModel_false.txt b/packages/genui/test/facade/prompt_builder_test.golden/create_and_update_with_dataModel_false.txt
index 145477889..bee29802b 100644
--- a/packages/genui/test/facade/prompt_builder_test.golden/create_and_update_with_dataModel_false.txt
+++ b/packages/genui/test/facade/prompt_builder_test.golden/create_and_update_with_dataModel_false.txt
@@ -117,7 +117,7 @@ To update an existing UI:
 -----OUTPUT_FORMAT_START-----
 When constructing UI, you must output a VALID A2UI JSON object representing one of the A2UI message types (`createSurface`, `updateComponents`).
 - You can treat the A2UI schema as a specification for the JSON you typically output.
-- You may include a brief conversational explanation before or after the JSON block if it helps the user, but the JSON block must be valid and complete.
+- The JSON block must be valid and complete.
 - Ensure your JSON is fenced with ```json and ```.
 -----OUTPUT_FORMAT_END-----
 
diff --git a/packages/genui/test/facade/prompt_builder_test.golden/create_and_update_with_dataModel_true.txt b/packages/genui/test/facade/prompt_builder_test.golden/create_and_update_with_dataModel_true.txt
index b2b15c822..0dda75d32 100644
--- a/packages/genui/test/facade/prompt_builder_test.golden/create_and_update_with_dataModel_true.txt
+++ b/packages/genui/test/facade/prompt_builder_test.golden/create_and_update_with_dataModel_true.txt
@@ -119,7 +119,7 @@ To update an existing UI:
 -----OUTPUT_FORMAT_START-----
 When constructing UI, you must output a VALID A2UI JSON object representing one of the A2UI message types (`createSurface`, `updateComponents`, `updateDataModel`).
 - You can treat the A2UI schema as a specification for the JSON you typically output.
-- You may include a brief conversational explanation before or after the JSON block if it helps the user, but the JSON block must be valid and complete.
+- The JSON block must be valid and complete.
 - Ensure your JSON is fenced with ```json and ```.
 -----OUTPUT_FORMAT_END-----
 
diff --git a/packages/genui/test/facade/prompt_builder_test.golden/create_only_with_dataModel_false.txt b/packages/genui/test/facade/prompt_builder_test.golden/create_only_with_dataModel_false.txt
index 9a0f4105c..d1e86c383 100644
--- a/packages/genui/test/facade/prompt_builder_test.golden/create_only_with_dataModel_false.txt
+++ b/packages/genui/test/facade/prompt_builder_test.golden/create_only_with_dataModel_false.txt
@@ -116,7 +116,7 @@ IMPORTANT: DO NOT update or modify surfaces created in previous turns. If the UI
 -----OUTPUT_FORMAT_START-----
 When constructing UI, you must output a VALID A2UI JSON object representing one of the A2UI message types (`createSurface`, `updateComponents`).
 - You can treat the A2UI schema as a specification for the JSON you typically output.
-- You may include a brief conversational explanation before or after the JSON block if it helps the user, but the JSON block must be valid and complete.
+- The JSON block must be valid and complete.
 - Ensure your JSON is fenced with ```json and ```.
 -----OUTPUT_FORMAT_END-----
 
diff --git a/packages/genui/test/facade/prompt_builder_test.golden/create_only_with_dataModel_true.txt b/packages/genui/test/facade/prompt_builder_test.golden/create_only_with_dataModel_true.txt
index a1f568bed..329b1b568 100644
--- a/packages/genui/test/facade/prompt_builder_test.golden/create_only_with_dataModel_true.txt
+++ b/packages/genui/test/facade/prompt_builder_test.golden/create_only_with_dataModel_true.txt
@@ -118,7 +118,7 @@ IMPORTANT: DO NOT update or modify surfaces created in previous turns. If the UI
 -----OUTPUT_FORMAT_START-----
 When constructing UI, you must output a VALID A2UI JSON object representing one of the A2UI message types (`createSurface`, `updateComponents`, `updateDataModel`).
 - You can treat the A2UI schema as a specification for the JSON you typically output.
-- You may include a brief conversational explanation before or after the JSON block if it helps the user, but the JSON block must be valid and complete.
+- The JSON block must be valid and complete.
 - Ensure your JSON is fenced with ```json and ```.
 -----OUTPUT_FORMAT_END-----
 
diff --git a/packages/genui/test/facade/prompt_builder_test.golden/update_only_with_dataModel_false.txt b/packages/genui/test/facade/prompt_builder_test.golden/update_only_with_dataModel_false.txt
index f9ebbb407..7e962fe86 100644
--- a/packages/genui/test/facade/prompt_builder_test.golden/update_only_with_dataModel_false.txt
+++ b/packages/genui/test/facade/prompt_builder_test.golden/update_only_with_dataModel_false.txt
@@ -109,7 +109,7 @@ To update an existing UI:
 -----OUTPUT_FORMAT_START-----
 When constructing UI, you must output a VALID A2UI JSON object representing one of the A2UI message types (`updateComponents`).
 - You can treat the A2UI schema as a specification for the JSON you typically output.
-- You may include a brief conversational explanation before or after the JSON block if it helps the user, but the JSON block must be valid and complete.
+- The JSON block must be valid and complete.
 - Ensure your JSON is fenced with ```json and ```.
 -----OUTPUT_FORMAT_END-----
 
diff --git a/packages/genui/test/facade/prompt_builder_test.golden/update_only_with_dataModel_true.txt b/packages/genui/test/facade/prompt_builder_test.golden/update_only_with_dataModel_true.txt
index 13b92963f..ad99d50ec 100644
--- a/packages/genui/test/facade/prompt_builder_test.golden/update_only_with_dataModel_true.txt
+++ b/packages/genui/test/facade/prompt_builder_test.golden/update_only_with_dataModel_true.txt
@@ -111,7 +111,7 @@ To update an existing UI:
 -----OUTPUT_FORMAT_START-----
 When constructing UI, you must output a VALID A2UI JSON object representing one of the A2UI message types (`updateComponents`, `updateDataModel`).
 - You can treat the A2UI schema as a specification for the JSON you typically output.
-- You may include a brief conversational explanation before or after the JSON block if it helps the user, but the JSON block must be valid and complete.
+- The JSON block must be valid and complete.
 - Ensure your JSON is fenced with ```json and ```.
 -----OUTPUT_FORMAT_END-----