[Frontend] Responses API MCP tools for built in tools and to pass through headers (#24628)

Signed-off-by: Alec Solder <alecs@fb.com>
Signed-off-by: Alec S <10566873+alecsolder@users.noreply.github.com>
Co-authored-by: Alec Solder <alecs@fb.com>
Co-authored-by: Ye (Charlotte) Qi <yeq@meta.com>

tests/entrypoints/openai/test_response_api_mcp_tools.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import pytest
+import pytest_asyncio
+from openai import OpenAI
+
+from ...utils import RemoteOpenAIServer
+
+MODEL_NAME = "openai/gpt-oss-20b"
+
+
+@pytest.fixture(scope="module")
+def monkeypatch_module():
+    from _pytest.monkeypatch import MonkeyPatch
+    mpatch = MonkeyPatch()
+    yield mpatch
+    mpatch.undo()
+
+
+@pytest.fixture(scope="module")
+def mcp_disabled_server(monkeypatch_module: pytest.MonkeyPatch):
+    args = ["--enforce-eager", "--tool-server", "demo"]
+
+    with monkeypatch_module.context() as m:
+        m.setenv("VLLM_ENABLE_RESPONSES_API_STORE", "1")
+        m.setenv("PYTHON_EXECUTION_BACKEND", "dangerously_use_uv")
+        with RemoteOpenAIServer(MODEL_NAME, args) as remote_server:
+            yield remote_server
+
+
+@pytest.fixture(scope="function")
+def mcp_enabled_server(monkeypatch_module: pytest.MonkeyPatch):
+    args = ["--enforce-eager", "--tool-server", "demo"]
+
+    with monkeypatch_module.context() as m:
+        m.setenv("VLLM_ENABLE_RESPONSES_API_STORE", "1")
+        m.setenv("PYTHON_EXECUTION_BACKEND", "dangerously_use_uv")
+        m.setenv("GPT_OSS_SYSTEM_TOOL_MCP_LABELS",
+                 "code_interpreter,container")
+        with RemoteOpenAIServer(MODEL_NAME, args) as remote_server:
+            yield remote_server
+
+
+@pytest_asyncio.fixture
+async def mcp_disabled_client(mcp_disabled_server):
+    async with mcp_disabled_server.get_async_client() as async_client:
+        yield async_client
+
+
+@pytest_asyncio.fixture
+async def mcp_enabled_client(mcp_enabled_server):
+    async with mcp_enabled_server.get_async_client() as async_client:
+        yield async_client
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("model_name", [MODEL_NAME])
+@pytest.mark.skip(reason="Code interpreter tool is not available in CI yet.")
+async def test_mcp_tool_env_flag_enabled(mcp_enabled_client: OpenAI,
+                                         model_name: str):
+    response = await mcp_enabled_client.responses.create(
+        model=model_name,
+        # TODO: Ideally should be able to set max tool calls
+        # to prevent multi-turn, but it is not currently supported
+        # would speed up the test
+        input=("What's the first 4 digits after the decimal point of "
+               "cube root of `19910212 * 20250910`? "
+               "Show only the digits. The python interpreter is not stateful "
+               "and you must print to see the output."),
+        tools=[{
+            "type": "mcp",
+            "server_label": "code_interpreter",
+            # URL unused for DemoToolServer
+            "server_url": "http://localhost:8888"
+        }],
+    )
+    assert response is not None
+    assert response.status == "completed"
+    assert response.usage.output_tokens_details.tool_output_tokens > 0
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("model_name", [MODEL_NAME])
+@pytest.mark.skip(reason="Code interpreter tool is not available in CI yet.")
+async def test_mcp_tool_env_flag_disabled(mcp_disabled_client: OpenAI,
+                                          model_name: str):
+    response = await mcp_disabled_client.responses.create(
+        model=model_name,
+        # TODO: Ideally should be able to set max tool calls
+        # to prevent multi-turn, but it is not currently supported
+        # would speed up the test
+        input=("What's the first 4 digits after the decimal point of "
+               "cube root of `19910212 * 20250910`? "
+               "Show only the digits. The python interpreter is not stateful "
+               "and you must print to see the output."),
+        tools=[{
+            "type": "mcp",
+            "server_label": "code_interpreter",
+            # URL unused for DemoToolServer
+            "server_url": "http://localhost:8888"
+        }],
+    )
+    assert response is not None
+    assert response.status == "completed"
+    assert response.usage.output_tokens_details.tool_output_tokens == 0

tests/entrypoints/openai/test_response_api_with_harmony.py

@@ -454,7 +454,13 @@ async def test_web_search(client: OpenAI, model_name: str):
 async def test_code_interpreter(client: OpenAI, model_name: str):
     response = await client.responses.create(
         model=model_name,
-        input="Multiply 64548*15151 using builtin python interpreter.",
+        # TODO: Ideally should be able to set max tool calls
+        # to prevent multi-turn, but it is not currently supported
+        # would speed up the test
+        input=("What's the first 4 digits after the decimal point of "
+               "cube root of `19910212 * 20250910`? "
+               "Show only the digits. The python interpreter is not stateful "
+               "and you must print to see the output."),
         tools=[{
             "type": "code_interpreter",
             "container": {
@@ -464,6 +470,7 @@ async def test_code_interpreter(client: OpenAI, model_name: str):
     )
     assert response is not None
     assert response.status == "completed"
+    assert response.usage.output_tokens_details.tool_output_tokens > 0
 
 
 def get_weather(latitude, longitude):

tests/test_envs.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import os
+from unittest.mock import patch
+
+import pytest
+
+from vllm.envs import env_list_with_choices, env_with_choices
+
+
+class TestEnvWithChoices:
+    """Test cases for env_with_choices function."""
+
+    def test_default_value_returned_when_env_not_set(self):
+        """Test default is returned when env var is not set."""
+        env_func = env_with_choices("NONEXISTENT_ENV", "default",
+                                    ["option1", "option2"])
+        assert env_func() == "default"
+
+    def test_none_default_returned_when_env_not_set(self):
+        """Test that None is returned when env not set and default is None."""
+        env_func = env_with_choices("NONEXISTENT_ENV", None,
+                                    ["option1", "option2"])
+        assert env_func() is None
+
+    def test_valid_value_returned_case_sensitive(self):
+        """Test that valid value is returned in case sensitive mode."""
+        with patch.dict(os.environ, {"TEST_ENV": "option1"}):
+            env_func = env_with_choices("TEST_ENV",
+                                        "default", ["option1", "option2"],
+                                        case_sensitive=True)
+            assert env_func() == "option1"
+
+    def test_valid_lowercase_value_returned_case_insensitive(self):
+        """Test that lowercase value is accepted in case insensitive mode."""
+        with patch.dict(os.environ, {"TEST_ENV": "option1"}):
+            env_func = env_with_choices("TEST_ENV",
+                                        "default", ["OPTION1", "OPTION2"],
+                                        case_sensitive=False)
+            assert env_func() == "option1"
+
+    def test_valid_uppercase_value_returned_case_insensitive(self):
+        """Test that uppercase value is accepted in case insensitive mode."""
+        with patch.dict(os.environ, {"TEST_ENV": "OPTION1"}):
+            env_func = env_with_choices("TEST_ENV",
+                                        "default", ["option1", "option2"],
+                                        case_sensitive=False)
+            assert env_func() == "OPTION1"
+
+    def test_invalid_value_raises_error_case_sensitive(self):
+        """Test that invalid value raises ValueError in case sensitive mode."""
+        with patch.dict(os.environ, {"TEST_ENV": "invalid"}):
+            env_func = env_with_choices("TEST_ENV",
+                                        "default", ["option1", "option2"],
+                                        case_sensitive=True)
+            with pytest.raises(ValueError,
+                               match="Invalid value 'invalid' for TEST_ENV"):
+                env_func()
+
+    def test_case_mismatch_raises_error_case_sensitive(self):
+        """Test that case mismatch raises ValueError in case sensitive mode."""
+        with patch.dict(os.environ, {"TEST_ENV": "OPTION1"}):
+            env_func = env_with_choices("TEST_ENV",
+                                        "default", ["option1", "option2"],
+                                        case_sensitive=True)
+            with pytest.raises(ValueError,
+                               match="Invalid value 'OPTION1' for TEST_ENV"):
+                env_func()
+
+    def test_invalid_value_raises_error_case_insensitive(self):
+        """Test that invalid value raises ValueError when case insensitive."""
+        with patch.dict(os.environ, {"TEST_ENV": "invalid"}):
+            env_func = env_with_choices("TEST_ENV",
+                                        "default", ["option1", "option2"],
+                                        case_sensitive=False)
+            with pytest.raises(ValueError,
+                               match="Invalid value 'invalid' for TEST_ENV"):
+                env_func()
+
+    def test_callable_choices_resolved_correctly(self):
+        """Test that callable choices are resolved correctly."""
+
+        def get_choices():
+            return ["dynamic1", "dynamic2"]
+
+        with patch.dict(os.environ, {"TEST_ENV": "dynamic1"}):
+            env_func = env_with_choices("TEST_ENV", "default", get_choices)
+            assert env_func() == "dynamic1"
+
+    def test_callable_choices_with_invalid_value(self):
+        """Test that callable choices raise error for invalid values."""
+
+        def get_choices():
+            return ["dynamic1", "dynamic2"]
+
+        with patch.dict(os.environ, {"TEST_ENV": "invalid"}):
+            env_func = env_with_choices("TEST_ENV", "default", get_choices)
+            with pytest.raises(ValueError,
+                               match="Invalid value 'invalid' for TEST_ENV"):
+                env_func()
+
+
+class TestEnvListWithChoices:
+    """Test cases for env_list_with_choices function."""
+
+    def test_default_list_returned_when_env_not_set(self):
+        """Test that default list is returned when env var is not set."""
+        env_func = env_list_with_choices("NONEXISTENT_ENV",
+                                         ["default1", "default2"],
+                                         ["option1", "option2"])
+        assert env_func() == ["default1", "default2"]
+
+    def test_empty_default_list_returned_when_env_not_set(self):
+        """Test that empty default list is returned when env not set."""
+        env_func = env_list_with_choices("NONEXISTENT_ENV", [],
+                                         ["option1", "option2"])
+        assert env_func() == []
+
+    def test_single_valid_value_parsed_correctly(self):
+        """Test that single valid value is parsed correctly."""
+        with patch.dict(os.environ, {"TEST_ENV": "option1"}):
+            env_func = env_list_with_choices("TEST_ENV", [],
+                                             ["option1", "option2"])
+            assert env_func() == ["option1"]
+
+    def test_multiple_valid_values_parsed_correctly(self):
+        """Test that multiple valid values are parsed correctly."""
+        with patch.dict(os.environ, {"TEST_ENV": "option1,option2"}):
+            env_func = env_list_with_choices("TEST_ENV", [],
+                                             ["option1", "option2"])
+            assert env_func() == ["option1", "option2"]
+
+    def test_values_with_whitespace_trimmed(self):
+        """Test that values with whitespace are trimmed correctly."""
+        with patch.dict(os.environ, {"TEST_ENV": " option1 , option2 "}):
+            env_func = env_list_with_choices("TEST_ENV", [],
+                                             ["option1", "option2"])
+            assert env_func() == ["option1", "option2"]
+
+    def test_empty_values_filtered_out(self):
+        """Test that empty values are filtered out."""
+        with patch.dict(os.environ, {"TEST_ENV": "option1,,option2,"}):
+            env_func = env_list_with_choices("TEST_ENV", [],
+                                             ["option1", "option2"])
+            assert env_func() == ["option1", "option2"]
+
+    def test_empty_string_returns_default(self):
+        """Test that empty string returns default."""
+        with patch.dict(os.environ, {"TEST_ENV": ""}):
+            env_func = env_list_with_choices("TEST_ENV", ["default"],
+                                             ["option1", "option2"])
+            assert env_func() == ["default"]
+
+    def test_only_commas_returns_default(self):
+        """Test that string with only commas returns default."""
+        with patch.dict(os.environ, {"TEST_ENV": ",,,"}):
+            env_func = env_list_with_choices("TEST_ENV", ["default"],
+                                             ["option1", "option2"])
+            assert env_func() == ["default"]
+
+    def test_case_sensitive_validation(self):
+        """Test case sensitive validation."""
+        with patch.dict(os.environ, {"TEST_ENV": "option1,OPTION2"}):
+            env_func = env_list_with_choices("TEST_ENV", [],
+                                             ["option1", "option2"],
+                                             case_sensitive=True)
+            with pytest.raises(ValueError,
+                               match="Invalid value 'OPTION2' in TEST_ENV"):
+                env_func()
+
+    def test_case_insensitive_validation(self):
+        """Test case insensitive validation."""
+        with patch.dict(os.environ, {"TEST_ENV": "OPTION1,option2"}):
+            env_func = env_list_with_choices("TEST_ENV", [],
+                                             ["option1", "option2"],
+                                             case_sensitive=False)
+            assert env_func() == ["OPTION1", "option2"]
+
+    def test_invalid_value_in_list_raises_error(self):
+        """Test that invalid value in list raises ValueError."""
+        with patch.dict(os.environ, {"TEST_ENV": "option1,invalid,option2"}):
+            env_func = env_list_with_choices("TEST_ENV", [],
+                                             ["option1", "option2"])
+            with pytest.raises(ValueError,
+                               match="Invalid value 'invalid' in TEST_ENV"):
+                env_func()
+
+    def test_callable_choices_resolved_correctly(self):
+        """Test that callable choices are resolved correctly."""
+
+        def get_choices():
+            return ["dynamic1", "dynamic2"]
+
+        with patch.dict(os.environ, {"TEST_ENV": "dynamic1,dynamic2"}):
+            env_func = env_list_with_choices("TEST_ENV", [], get_choices)
+            assert env_func() == ["dynamic1", "dynamic2"]
+
+    def test_callable_choices_with_invalid_value(self):
+        """Test that callable choices raise error for invalid values."""
+
+        def get_choices():
+            return ["dynamic1", "dynamic2"]
+
+        with patch.dict(os.environ, {"TEST_ENV": "dynamic1,invalid"}):
+            env_func = env_list_with_choices("TEST_ENV", [], get_choices)
+            with pytest.raises(ValueError,
+                               match="Invalid value 'invalid' in TEST_ENV"):
+                env_func()
+
+    def test_duplicate_values_preserved(self):
+        """Test that duplicate values in the list are preserved."""
+        with patch.dict(os.environ, {"TEST_ENV": "option1,option1,option2"}):
+            env_func = env_list_with_choices("TEST_ENV", [],
+                                             ["option1", "option2"])
+            assert env_func() == ["option1", "option1", "option2"]

vllm/entrypoints/context.py

@@ -8,6 +8,7 @@ from abc import ABC, abstractmethod
 from contextlib import AsyncExitStack
 from typing import TYPE_CHECKING, Optional, Union
 
+from openai.types.responses.tool import Mcp
 from openai_harmony import Author, Message, Role, StreamState, TextContent
 
 from vllm.entrypoints.harmony_utils import (
@@ -21,6 +22,24 @@ if TYPE_CHECKING:
 
 logger = logging.getLogger(__name__)
 
+# This is currently needed as the tool type doesn't 1:1 match the
+# tool namespace, which is what is used to look up the
+# connection to the tool server
+_TOOL_NAME_TO_TYPE_MAP = {
+    "browser": "web_search_preview",
+    "python": "code_interpreter",
+    "container": "container",
+}
+
+
+def _map_tool_name_to_tool_type(tool_name: str) -> str:
+    if tool_name not in _TOOL_NAME_TO_TYPE_MAP:
+        available_tools = ', '.join(_TOOL_NAME_TO_TYPE_MAP.keys())
+        raise ValueError(
+            f"Built-in tool name '{tool_name}' not defined in mapping. "
+            f"Available tools: {available_tools}")
+    return _TOOL_NAME_TO_TYPE_MAP[tool_name]
+
 
 class TurnTokens:
     """Tracks token counts for a single conversation turn."""
@@ -59,8 +78,8 @@ class ConversationContext(ABC):
 
     @abstractmethod
     async def init_tool_sessions(self, tool_server: Optional[ToolServer],
-                                 exit_stack: AsyncExitStack,
-                                 request_id: str) -> None:
+                                 exit_stack: AsyncExitStack, request_id: str,
+                                 mcp_tools: dict[str, Mcp]) -> None:
         pass
 
     @abstractmethod
@@ -96,8 +115,8 @@ class SimpleContext(ConversationContext):
         raise NotImplementedError("Should not be called.")
 
     async def init_tool_sessions(self, tool_server: Optional[ToolServer],
-                                 exit_stack: AsyncExitStack,
-                                 request_id: str) -> None:
+                                 exit_stack: AsyncExitStack, request_id: str,
+                                 mcp_tools: dict[str, Mcp]) -> None:
         pass
 
     async def cleanup_session(self) -> None:
@@ -318,13 +337,17 @@ class HarmonyContext(ConversationContext):
         ]
 
     async def init_tool_sessions(self, tool_server: Optional[ToolServer],
-                                 exit_stack: AsyncExitStack,
-                                 request_id: str) -> None:
+                                 exit_stack: AsyncExitStack, request_id: str,
+                                 mcp_tools: dict[str, Mcp]):
         if tool_server:
             for tool_name in self.available_tools:
                 if tool_name not in self._tool_sessions:
+                    tool_type = _map_tool_name_to_tool_type(tool_name)
+                    headers = mcp_tools[
+                        tool_type].headers if tool_type in mcp_tools else None
                     tool_session = await exit_stack.enter_async_context(
-                        tool_server.new_session(tool_name, request_id))
+                        tool_server.new_session(tool_name, request_id,
+                                                headers))
                     self._tool_sessions[tool_name] = tool_session
                     exit_stack.push_async_exit(self.cleanup_session)
 

vllm/entrypoints/harmony_utils.py

@@ -126,8 +126,10 @@ def get_developer_message(
         function_tools: list[Union[Tool, ChatCompletionToolsParam]] = []
         for tool in tools:
             if tool.type in ("web_search_preview", "code_interpreter",
-                             "container"):
+                             "container", "mcp"):
                 # These are built-in tools that are added to the system message.
+                # Adding in MCP for now until we support MCP tools executed
+                # server side
                 pass
 
             elif tool.type == "function":

vllm/entrypoints/openai/serving_responses.py

@@ -460,8 +460,12 @@ class OpenAIServingResponses(OpenAIServing):
 
         async with AsyncExitStack() as exit_stack:
             try:
+                mcp_tools = {
+                    tool.server_label: tool
+                    for tool in request.tools if tool.type == "mcp"
+                }
                 await context.init_tool_sessions(self.tool_server, exit_stack,
-                                                 request.request_id)
+                                                 request.request_id, mcp_tools)
                 async for _ in result_generator:
                     pass
             except asyncio.CancelledError:
@@ -748,11 +752,16 @@ class OpenAIServingResponses(OpenAIServing):
             # New conversation.
             reasoning_effort = (request.reasoning.effort
                                 if request.reasoning else None)
-            # Temporary: OpenAI types doesn't have container tool
-            # so we used MCP to cover that, up for change
             tool_types = [tool.type for tool in request.tools]
-            if envs.VLLM_GPT_OSS_USE_CONTAINER_TOOL:
-                tool_types.append("container")
+
+            # Allow the MCP Tool type to enable built in tools if the
+            # server_label is allowlisted in
+            # envs.GPT_OSS_SYSTEM_TOOL_MCP_LABELS
+            if envs.GPT_OSS_SYSTEM_TOOL_MCP_LABELS:
+                for tool in request.tools:
+                    if (tool.type == "mcp" and tool.server_label
+                            in envs.GPT_OSS_SYSTEM_TOOL_MCP_LABELS):
+                        tool_types.append(tool.server_label)
             enable_browser = ("web_search_preview" in tool_types
                               and self.tool_server is not None
                               and self.tool_server.has_tool("browser"))
@@ -1653,8 +1662,12 @@ class OpenAIServingResponses(OpenAIServing):
         async with AsyncExitStack() as exit_stack:
             processer = None
             if self.use_harmony:
+                mcp_tools = {
+                    tool.server_label: tool
+                    for tool in request.tools if tool.type == "mcp"
+                }
                 await context.init_tool_sessions(self.tool_server, exit_stack,
-                                                 request.request_id)
+                                                 request.request_id, mcp_tools)
                 processer = self._process_harmony_streaming_events
             else:
                 processer = self._process_simple_streaming_events

vllm/entrypoints/tool_server.py

@@ -18,7 +18,6 @@ if TYPE_CHECKING:
 async def list_server_and_tools(server_url: str):
     from mcp import ClientSession
     from mcp.client.sse import sse_client
-
     async with sse_client(url=server_url) as streams, ClientSession(
             *streams) as session:
         initialize_response = await session.initialize()
@@ -86,8 +85,12 @@ class ToolServer(ABC):
         pass
 
     @abstractmethod
-    def new_session(self, tool_name: str,
-                    session_id: str) -> AbstractAsyncContextManager[Any]:
+    def new_session(
+        self,
+        tool_name: str,
+        session_id: str,
+        headers: Optional[dict[str, str]] = None
+    ) -> AbstractAsyncContextManager[Any]:
         """
         Create a session for the tool.
         """
@@ -144,15 +147,20 @@ class MCPToolServer(ToolServer):
         return self.harmony_tool_descriptions.get(tool_name)
 
     @asynccontextmanager
-    async def new_session(self, tool_name: str, session_id: str):
+    async def new_session(self,
+                          tool_name: str,
+                          session_id: str,
+                          headers: Optional[dict[str, str]] = None):
         from mcp import ClientSession
         from mcp.client.sse import sse_client
         url = self.urls.get(tool_name)
-        headers = {"x-session-id": session_id}
+        request_headers = {"x-session-id": session_id}
+        if headers is not None:
+            request_headers.update(headers)
         if not url:
             raise KeyError(f"Tool '{tool_name}' is not supported")
-        async with sse_client(url=url,
-                              headers=headers) as streams, ClientSession(
+        async with sse_client(
+                url=url, headers=request_headers) as streams, ClientSession(
                     *streams) as session:
             await session.initialize()
             yield session
@@ -189,7 +197,10 @@ class DemoToolServer(ToolServer):
             raise ValueError(f"Unknown tool {tool_name}")
 
     @asynccontextmanager
-    async def new_session(self, tool_name: str, session_id: str):
+    async def new_session(self,
+                          tool_name: str,
+                          session_id: str,
+                          headers: Optional[dict[str, str]] = None):
         if tool_name not in self.tools:
             raise KeyError(f"Tool '{tool_name}' is not supported")
         yield self.tools[tool_name]

vllm/envs.py

@@ -185,11 +185,11 @@ if TYPE_CHECKING:
     VLLM_ALLREDUCE_USE_SYMM_MEM: bool = False
     VLLM_TUNED_CONFIG_FOLDER: Optional[str] = None
     VLLM_DISABLE_PAD_FOR_CUDAGRAPH: bool = False
-    VLLM_GPT_OSS_USE_CONTAINER_TOOL: bool = False
     VLLM_GPT_OSS_HARMONY_SYSTEM_INSTRUCTIONS: bool = False
     VLLM_CUSTOM_SCOPES_FOR_PROFILING: bool = False
     VLLM_KV_EVENTS_USE_INT_BLOCK_HASHES: bool = True
     VLLM_OBJECT_STORAGE_SHM_BUFFER_NAME: str = "VLLM_OBJECT_STORAGE_SHM_BUFFER"
+    GPT_OSS_SYSTEM_TOOL_MCP_LABELS: list[str] = []
     VLLM_PATTERN_MATCH_DEBUG: Optional[str] = None
 
 
@@ -261,6 +261,58 @@ def env_with_choices(
     return _get_validated_env
 
 
+def env_list_with_choices(
+        env_name: str,
+        default: list[str],
+        choices: Union[list[str], Callable[[], list[str]]],
+        case_sensitive: bool = True) -> Callable[[], list[str]]:
+    """
+    Create a lambda that validates environment variable 
+    containing comma-separated values against allowed choices
+    
+    Args:
+        env_name: Name of the environment variable
+        default: Default list of values if not set
+        choices: List of valid string options or callable that returns list
+        case_sensitive: Whether validation should be case sensitive
+        
+    Returns:
+        Lambda function for environment_variables
+        dict that returns list of strings
+    """
+
+    def _get_validated_env_list() -> list[str]:
+        value = os.getenv(env_name)
+        if value is None:
+            return default
+
+        # Split comma-separated values and strip whitespace
+        values = [v.strip() for v in value.split(",") if v.strip()]
+
+        if not values:
+            return default
+
+        # Resolve choices if it's a callable (for lazy loading)
+        actual_choices = choices() if callable(choices) else choices
+
+        # Validate each value
+        for val in values:
+            if not case_sensitive:
+                check_value = val.lower()
+                check_choices = [choice.lower() for choice in actual_choices]
+            else:
+                check_value = val
+                check_choices = actual_choices
+
+            if check_value not in check_choices:
+                raise ValueError(f"Invalid value '{val}' in {env_name}. "
+                                 f"Valid options: {actual_choices}.")
+
+        return values
+
+    return _get_validated_env_list
+
+
 def get_vllm_port() -> Optional[int]:
     """Get the port from VLLM_PORT environment variable.
 
@@ -1320,10 +1372,6 @@ environment_variables: dict[str, Callable[[], Any]] = {
     "VLLM_TUNED_CONFIG_FOLDER":
     lambda: os.getenv("VLLM_TUNED_CONFIG_FOLDER", None),
 
-    # Allows vllm use container tool
-    "VLLM_GPT_OSS_USE_CONTAINER_TOOL":
-    lambda: bool(int(os.getenv("VLLM_GPT_OSS_USE_CONTAINER_TOOL", "0"))),
-
     # Allows harmony instructions to be injected on system messages
     "VLLM_GPT_OSS_HARMONY_SYSTEM_INSTRUCTIONS":
     lambda: bool(
@@ -1343,6 +1391,14 @@ environment_variables: dict[str, Callable[[], Any]] = {
     "VLLM_OBJECT_STORAGE_SHM_BUFFER_NAME":
     lambda: os.getenv("VLLM_OBJECT_STORAGE_SHM_BUFFER_NAME",
                       "VLLM_OBJECT_STORAGE_SHM_BUFFER"),
+
+    # Valid values are container,code_interpreter,web_search_preview
+    # ex GPT_OSS_SYSTEM_TOOL_MCP_LABELS=container,code_interpreter
+    "GPT_OSS_SYSTEM_TOOL_MCP_LABELS":
+    env_list_with_choices("GPT_OSS_SYSTEM_TOOL_MCP_LABELS", [],
+                            ["container",
+                            "code_interpreter",
+                            "web_search_preview"]),
 }
 
 # --8<-- [end:env-vars-definition]