feat: add tool metadata in FastMCP.tool decorator

src/mcp/server/fastmcp/server.py

@@ -4,7 +4,14 @@
 
 import inspect
 import re
-from collections.abc import AsyncIterator, Awaitable, Callable, Collection, Iterable, Sequence
+from collections.abc import (
+    AsyncIterator,
+    Awaitable,
+    Callable,
+    Collection,
+    Iterable,
+    Sequence,
+)
 from contextlib import AbstractAsyncContextManager, asynccontextmanager
 from typing import Any, Generic, Literal
 
@@ -22,10 +29,21 @@
 from starlette.types import Receive, Scope, Send
 
 from mcp.server.auth.middleware.auth_context import AuthContextMiddleware
-from mcp.server.auth.middleware.bearer_auth import BearerAuthBackend, RequireAuthMiddleware
-from mcp.server.auth.provider import OAuthAuthorizationServerProvider, ProviderTokenVerifier, TokenVerifier
+from mcp.server.auth.middleware.bearer_auth import (
+    BearerAuthBackend,
+    RequireAuthMiddleware,
+)
+from mcp.server.auth.provider import (
+    OAuthAuthorizationServerProvider,
+    ProviderTokenVerifier,
+    TokenVerifier,
+)
 from mcp.server.auth.settings import AuthSettings
-from mcp.server.elicitation import ElicitationResult, ElicitSchemaModelT, elicit_with_validation
+from mcp.server.elicitation import (
+    ElicitationResult,
+    ElicitSchemaModelT,
+    elicit_with_validation,
+)
 from mcp.server.fastmcp.exceptions import ResourceError
 from mcp.server.fastmcp.prompts import Prompt, PromptManager
 from mcp.server.fastmcp.resources import FunctionResource, Resource, ResourceManager
@@ -112,7 +130,9 @@ def lifespan_wrapper(
     lifespan: Callable[[FastMCP[LifespanResultT]], AbstractAsyncContextManager[LifespanResultT]],
 ) -> Callable[[MCPServer[LifespanResultT, Request]], AbstractAsyncContextManager[LifespanResultT]]:
     @asynccontextmanager
-    async def wrap(_: MCPServer[LifespanResultT, Request]) -> AsyncIterator[LifespanResultT]:
+    async def wrap(
+        _: MCPServer[LifespanResultT, Request],
+    ) -> AsyncIterator[LifespanResultT]:
         async with lifespan(app) as context:
             yield context
 
@@ -126,7 +146,7 @@ def __init__(  # noqa: PLR0913
         instructions: str | None = None,
         website_url: str | None = None,
         icons: list[Icon] | None = None,
-        auth_server_provider: OAuthAuthorizationServerProvider[Any, Any, Any] | None = None,
+        auth_server_provider: (OAuthAuthorizationServerProvider[Any, Any, Any] | None) = None,
         token_verifier: TokenVerifier | None = None,
         event_store: EventStore | None = None,
         *,
@@ -145,7 +165,7 @@ def __init__(  # noqa: PLR0913
         warn_on_duplicate_tools: bool = True,
         warn_on_duplicate_prompts: bool = True,
         dependencies: Collection[str] = (),
-        lifespan: Callable[[FastMCP[LifespanResultT]], AbstractAsyncContextManager[LifespanResultT]] | None = None,
+        lifespan: (Callable[[FastMCP[LifespanResultT]], AbstractAsyncContextManager[LifespanResultT]] | None) = None,
         auth: AuthSettings | None = None,
         transport_security: TransportSecuritySettings | None = None,
     ):
@@ -290,6 +310,7 @@ async def list_tools(self) -> list[MCPTool]:
                 outputSchema=info.output_schema,
                 annotations=info.annotations,
                 icons=info.icons,
+                _meta=info.meta,
             )
             for info in tools
         ]
@@ -363,6 +384,7 @@ def add_tool(
         description: str | None = None,
         annotations: ToolAnnotations | None = None,
         icons: list[Icon] | None = None,
+        meta: dict[str, Any] | None = None,
         structured_output: bool | None = None,
     ) -> None:
         """Add a tool to the server.
@@ -388,6 +410,7 @@ def add_tool(
             description=description,
             annotations=annotations,
             icons=icons,
+            meta=meta,
             structured_output=structured_output,
         )
 
@@ -409,6 +432,7 @@ def tool(
         description: str | None = None,
         annotations: ToolAnnotations | None = None,
         icons: list[Icon] | None = None,
+        meta: dict[str, Any] | None = None,
         structured_output: bool | None = None,
     ) -> Callable[[AnyFunction], AnyFunction]:
         """Decorator to register a tool.
@@ -456,6 +480,7 @@ def decorator(fn: AnyFunction) -> AnyFunction:
                 description=description,
                 annotations=annotations,
                 icons=icons,
+                meta=meta,
                 structured_output=structured_output,
             )
             return fn
@@ -1164,7 +1189,10 @@ async def elicit(
         """
 
         return await elicit_with_validation(
-            session=self.request_context.session, message=message, schema=schema, related_request_id=self.request_id
+            session=self.request_context.session,
+            message=message,
+            schema=schema,
+            related_request_id=self.request_id,
         )
 
     async def log(

src/mcp/server/fastmcp/tools/base.py

@@ -34,6 +34,7 @@ class Tool(BaseModel):
     context_kwarg: str | None = Field(None, description="Name of the kwarg that should receive context")
     annotations: ToolAnnotations | None = Field(None, description="Optional annotations for the tool")
     icons: list[Icon] | None = Field(default=None, description="Optional list of icons for this tool")
+    meta: dict[str, Any] | None = Field(default=None, description="Optional metadata for this tool")
 
     @cached_property
     def output_schema(self) -> dict[str, Any] | None:
@@ -49,6 +50,7 @@ def from_function(
         context_kwarg: str | None = None,
         annotations: ToolAnnotations | None = None,
         icons: list[Icon] | None = None,
+        meta: dict[str, Any] | None = None,
         structured_output: bool | None = None,
     ) -> Tool:
         """Create a Tool from a function."""
@@ -81,6 +83,7 @@ def from_function(
             context_kwarg=context_kwarg,
             annotations=annotations,
             icons=icons,
+            meta=meta,
         )
 
     async def run(

src/mcp/server/fastmcp/tools/tool_manager.py

@@ -50,6 +50,7 @@ def add_tool(
         description: str | None = None,
         annotations: ToolAnnotations | None = None,
         icons: list[Icon] | None = None,
+        meta: dict[str, Any] | None = None,
         structured_output: bool | None = None,
     ) -> Tool:
         """Add a tool to the server."""
@@ -60,6 +61,7 @@ def add_tool(
             description=description,
             annotations=annotations,
             icons=icons,
+            meta=meta,
             structured_output=structured_output,
         )
         existing = self._tools.get(tool.name)