diff --git a/backend/open_webui/tools/builtin.py b/backend/open_webui/tools/builtin.py
index 2b28f46846..29000b5d30 100644
--- a/backend/open_webui/tools/builtin.py
+++ b/backend/open_webui/tools/builtin.py
@@ -2909,7 +2909,8 @@ async def view_file(
             return JSONCodec.dumps(result, ensure_ascii=False)
 
         sliced = content[offset : offset + max_chars]
-        is_truncated = (offset + len(sliced)) < total_chars
+        returned_chars = len(sliced)
+        is_truncated = (offset + returned_chars) < total_chars
 
         if line_numbers:
             start_ln = content[:offset].count('\n') + 1
@@ -2927,10 +2928,10 @@ async def view_file(
         if is_truncated or offset > 0:
             result['truncated'] = is_truncated
             result['total_chars'] = total_chars
-            result['returned_chars'] = len(sliced)
+            result['returned_chars'] = returned_chars
             result['offset'] = offset
             if is_truncated:
-                result['next_offset'] = offset + len(sliced)
+                result['next_offset'] = offset + returned_chars
 
         return JSONCodec.dumps(result, ensure_ascii=False)
     except Exception as e:
@@ -3052,7 +3053,8 @@ async def view_knowledge_file(
             return JSONCodec.dumps(result, ensure_ascii=False)
 
         sliced = content[offset : offset + max_chars]
-        is_truncated = (offset + len(sliced)) < total_chars
+        returned_chars = len(sliced)
+        is_truncated = (offset + returned_chars) < total_chars
 
         if line_numbers:
             start_ln = content[:offset].count('\n') + 1
@@ -3073,10 +3075,10 @@ async def view_knowledge_file(
         if is_truncated or offset > 0:
             result['truncated'] = is_truncated
             result['total_chars'] = total_chars
-            result['returned_chars'] = len(sliced)
+            result['returned_chars'] = returned_chars
             result['offset'] = offset
             if is_truncated:
-                result['next_offset'] = offset + len(sliced)
+                result['next_offset'] = offset + returned_chars
 
         return JSONCodec.dumps(result, ensure_ascii=False)
     except Exception as e: