No way to declare input schema for tools using Fast MCP #323
Description
There appears to be no clear cut way to add an input_schema into a tool when declaring an MCP server using the FastMCP initiator.
the tool decorator within the FastMCP class has no way to initialize an input schema.
def tool(
self, name: str | None = None, description: str | None = None
) -> Callable[[AnyFunction], AnyFunction]:
# Check if user passed function directly instead of calling decorator
if callable(name):
raise TypeError(
"The @tool decorator was used incorrectly. "
"Did you forget to call it? Use @tool() instead of @tool"
)
def decorator(fn: AnyFunction) -> AnyFunction:
self.add_tool(fn, name=name, description=description)
return fn
return decorator
while the tool object its self has a input schema attribute
class Tool(BaseModel):
name: str
"""The name of the tool."""
description: str | None = None
"""A human-readable description of the tool."""
inputSchema: dict[str, Any]
"""A JSON Schema object defining the expected parameters for the tool."""
model_config = ConfigDict(extra="allow")
the tool manager within fastMCP also has no way of inputting a schema when using add_tool
class ToolManager:
def __init__(self, warn_on_duplicate_tools: bool = True):
self._tools: dict[str, Tool] = {}
self.warn_on_duplicate_tools = warn_on_duplicate_tools
def get_tool(self, name: str) -> Tool | None:
"""Get tool by name."""
return self._tools.get(name)
def list_tools(self) -> list[Tool]:
"""List all registered tools."""
return list(self._tools.values())
def add_tool(
self,
fn: Callable,
name: str | None = None,
description: str | None = None,
) -> Tool:
"""Add a tool to the server."""
tool = Tool.from_function(fn, name=name, description=description)
existing = self._tools.get(tool.name)
if existing:
if self.warn_on_duplicate_tools:
logger.warning(f"Tool already exists: {tool.name}")
return existing
self._tools[tool.name] = tool
return tool
async def call_tool(
self,
name: str,
arguments: dict[str, Any],
context: Context[ServerSessionT, LifespanContextT] | None = None,
) -> Any:
"""Call a tool by name with arguments."""
tool = self.get_tool(name)
if not tool:
raise ToolError(f"Unknown tool: {name}")
return await tool.run(arguments, context=context)
would it be possible to input the schema within the tool decorator so it would look something like this
@mcp.tool(input_schema=(json string of schema))
def check_availability(state: str, token: str, user: str, timeZone: str = None) -> str:
#rest of the code