feat: Implement SEP-986: Tool Name Guidance

Author: vincent0426

src/mcp/types.py

@@ -1,7 +1,8 @@
 from collections.abc import Callable
+import re
 from typing import Annotated, Any, Generic, Literal, TypeAlias, TypeVar
 
-from pydantic import BaseModel, ConfigDict, Field, FileUrl, RootModel
+from pydantic import BaseModel, ConfigDict, Field, FileUrl, RootModel, field_validator
 from pydantic.networks import AnyUrl, UrlConstraints
 from typing_extensions import deprecated
 
@@ -39,6 +40,10 @@
 RequestId = Annotated[int, Field(strict=True)] | str
 AnyFunction: TypeAlias = Callable[..., Any]
 
+# Tool name validation pattern (ASCII letters, digits, underscore, dash, dot)
+# Pattern ensures entire string contains only valid characters by using ^ and $ anchors
+TOOL_NAME_PATTERN = re.compile(r"^[A-Za-z0-9_.-]+$")
+
 
 class RequestParams(BaseModel):
     class Meta(BaseModel):
@@ -891,6 +896,22 @@ class Tool(BaseMetadata):
     """
     model_config = ConfigDict(extra="allow")
 
+    @field_validator("name")
+    @classmethod
+    def _validate_tool_name(cls, value: str) -> str:
+        if not (1 <= len(value) <= 128):
+            raise ValueError(f"Invalid tool name length: {len(value)}. Tool name must be between 1 and 128 characters.")
+
+        if not TOOL_NAME_PATTERN.fullmatch(value):
+            raise ValueError("Invalid tool name characters. Allowed: A-Z, a-z, 0-9, underscore (_), dash (-), dot (.).")
+
+        return value
+
+    """
+    See [MCP specification](https://modelcontextprotocol.io/specification/draft/server/tools#tool-names)
+    for more information on tool naming conventions.
+    """
+
 
 class ListToolsResult(PaginatedResult):
     """The server's response to a tools/list request from the client."""

tests/test_types.py

@@ -9,6 +9,7 @@
     InitializeRequestParams,
     JSONRPCMessage,
     JSONRPCRequest,
+    Tool,
 )
 
 
@@ -56,3 +57,37 @@ async def test_method_initialization():
     assert initialize_request.method == "initialize", "method should be set to 'initialize'"
     assert initialize_request.params is not None
     assert initialize_request.params.protocolVersion == LATEST_PROTOCOL_VERSION
+
+
+@pytest.mark.parametrize(
+    "name",
+    [
+        "getUser",
+        "DATA_EXPORT_v2",
+        "admin.tools.list",
+        "a",
+        "Z9_.-",
+        "x" * 128,  # max length
+    ],
+)
+def test_tool_allows_valid_names(name: str) -> None:
+    Tool(name=name, inputSchema={"type": "object"})
+
+
+@pytest.mark.parametrize(
+    ("name", "expected"),
+    [
+        ("", "Invalid tool name length: 0. Tool name must be between 1 and 128 characters."),
+        ("x" * 129, "Invalid tool name length: 129. Tool name must be between 1 and 128 characters."),
+        ("has space", "Invalid tool name characters. Allowed: A-Z, a-z, 0-9, underscore (_), dash (-), dot (.)."),
+        ("comma,name", "Invalid tool name characters. Allowed: A-Z, a-z, 0-9, underscore (_), dash (-), dot (.)."),
+        ("not/allowed", "Invalid tool name characters. Allowed: A-Z, a-z, 0-9, underscore (_), dash (-), dot (.)."),
+        ("name@", "Invalid tool name characters. Allowed: A-Z, a-z, 0-9, underscore (_), dash (-), dot (.)."),
+        ("name#", "Invalid tool name characters. Allowed: A-Z, a-z, 0-9, underscore (_), dash (-), dot (.)."),
+        ("name$", "Invalid tool name characters. Allowed: A-Z, a-z, 0-9, underscore (_), dash (-), dot (.)."),
+    ],
+)
+def test_tool_rejects_invalid_names(name: str, expected: str) -> None:
+    with pytest.raises(ValueError) as exc_info:
+        Tool(name=name, inputSchema={"type": "object"})
+    assert expected in str(exc_info.value)