Use OpenAPI 3.1.0 format for MCP Server JSON schemas (#182767)

homeassistant/components/mcp_server/server.py

@@ -44,7 +44,9 @@ def _format_tool(
 ) -> types.Tool:
     """Format tool specification."""
     input_schema = probatio.to_openapi(
-        tool.parameters, custom_serializer=custom_serializer
+        tool.parameters,
+        custom_serializer=custom_serializer,
+        openapi_version="3.1.0",
     )
     mcp_schema: dict[str, Any] = {
         "type": "object",

tests/components/mcp_server/test_http.py

@@ -687,6 +687,51 @@ async def test_mcp_tools_list_required_parameters(
     assert tool.inputSchema.get("required") == expected_required
 
 
+@pytest.mark.usefixtures("setup_integration")
+@pytest.mark.parametrize("llm_hass_api", [TEST_LLM_API_ID])
+@pytest.mark.parametrize(
+    ("parameters", "expected_schema"),
+    [
+        pytest.param(
+            probatio.Schema(
+                {probatio.Optional("value"): probatio.Range(min=0, min_included=False)}
+            ),
+            {"type": "number", "exclusiveMinimum": 0},
+            id="exclusive-minimum",
+        ),
+        pytest.param(
+            probatio.Schema({probatio.Optional("value"): probatio.Maybe(str)}),
+            {"anyOf": [{"type": "null"}, {"type": "string"}]},
+            id="nullable",
+        ),
+    ],
+)
+async def test_mcp_tools_list_json_schema(
+    hass: HomeAssistant,
+    mcp_url: str,
+    mcp_client: MCPClientFactory,
+    hass_supervisor_access_token: str,
+    parameters: probatio.Schema,
+    expected_schema: JsonObjectType,
+) -> None:
+    """Test tool parameters use JSON Schema 2020-12 compatible representations."""
+    llm.async_register_api(
+        hass,
+        MockLLMAPI(
+            hass=hass,
+            id=TEST_LLM_API_ID,
+            name="Test API",
+            tools=[_StubTool(parameters)],
+        ),
+    )
+
+    async with mcp_client(hass, mcp_url, hass_supervisor_access_token) as session:
+        result = await session.list_tools()
+
+    tool = next(tool for tool in result.tools if tool.name == "test_tool")
+    assert tool.inputSchema["properties"]["value"] == expected_schema
+
+
 @pytest.mark.parametrize("llm_hass_api", [TEST_LLM_API_ID])
 async def test_mcp_tools_list_metadata(
     hass: HomeAssistant,