diff --git a/jupyter_mcp_server/server.py b/jupyter_mcp_server/server.py
index 5c7d6a8..57a1349 100644
--- a/jupyter_mcp_server/server.py
+++ b/jupyter_mcp_server/server.py
@@ -410,7 +410,7 @@ async def execute_cell(
 
 @mcp.tool()
 async def insert_execute_code_cell(
-    cell_index: Annotated[int, Field(description="Index of the cell to insert and execute (0-based)", ge=0)],
+    cell_index: Annotated[int, Field(description="Index of the cell to insert and execute (0-based)", ge=-1)],
     cell_source: Annotated[str, Field(description="Code source for the cell")],
     timeout: Annotated[int, Field(description="Maximum seconds to wait for execution")] = 90,
 ) -> Annotated[list[str | ImageContent], Field(description="List of outputs from the executed cell")]:
@@ -743,4 +743,4 @@ async def get_registered_tools():
         
         tools.append(tool_dict)
     
-    return tools
\ No newline at end of file
+    return tools
diff --git a/jupyter_mcp_server/utils.py b/jupyter_mcp_server/utils.py
index be9d560..b6632fc 100644
--- a/jupyter_mcp_server/utils.py
+++ b/jupyter_mcp_server/utils.py
@@ -5,6 +5,7 @@
 import re
 import asyncio
 import time
+import json
 from typing import Any, Union
 from mcp.types import ImageContent
 from jupyter_mcp_server.config import ALLOW_IMG_OUTPUT
@@ -83,7 +84,9 @@ def extract_output(output: Union[dict, Any]) -> Union[str, ImageContent]:
         return strip_ansi_codes(str(text))
     
     elif output_type in ["display_data", "execute_result"]:
-        data = output.get("data", {})
+        
+        data = output.get("data", {})       
+        
         if "image/png" in data:
             if ALLOW_IMG_OUTPUT:
                 try:
@@ -93,6 +96,8 @@ def extract_output(output: Union[dict, Any]) -> Union[str, ImageContent]:
                     return "[Image Output (PNG) - Error processing image]"
             else:
                 return "[Image Output (PNG) - Image display disabled]"
+            
+
         if "text/plain" in data:
             plain_text = data["text/plain"]
             if hasattr(plain_text, 'source'):
@@ -943,4 +948,4 @@ async def get_notebook_model(serverapp: Any, notebook_path: str):
         return None
     nb = NotebookModel()
     nb._doc = ydoc
-    return nb
\ No newline at end of file
+    return nb
diff --git a/tests/test_tools.py b/tests/test_tools.py
index 2ca9acd..3288031 100644
--- a/tests/test_tools.py
+++ b/tests/test_tools.py
@@ -108,6 +108,11 @@ async def check_and_delete_cell(client: MCPClient, index, expected_type, content
         expected_result = eval(code_content)
         assert int(code_result['result'][0]) == expected_result
 
+        # Testing appending code cell to bottom of notebook
+        code_result = await mcp_client_parametrized.insert_execute_code_cell(-1, code_content)
+        expected_result = eval(code_content)
+        assert int(code_result['result'][0]) == expected_result
+
         # Test overwrite_cell_source
         new_code_content = f"({code_content}) * 2"
         result = await mcp_client_parametrized.overwrite_cell_source(1, new_code_content)
@@ -267,4 +272,4 @@ async def test_list_kernels(mcp_client_parametrized: MCPClient):
         kernel_list = await mcp_client_parametrized.list_kernels()
         logging.debug(f"Kernel list: {kernel_list}")
         # Check for either TSV header or "No kernels found" message
-        assert "ID\tName\tDisplay_Name\tLanguage\tState\tConnections\tLast_Activity\tEnvironment" in kernel_list
\ No newline at end of file
+        assert "ID\tName\tDisplay_Name\tLanguage\tState\tConnections\tLast_Activity\tEnvironment" in kernel_list