diff --git a/src/mcp/types.py b/src/mcp/types.py
index 2c27f83..ad141d4 100644
--- a/src/mcp/types.py
+++ b/src/mcp/types.py
@@ -657,7 +657,7 @@ class Tool(BaseModel):
     """The name of the tool."""
     description: str | None = None
     """A human-readable description of the tool."""
-    inputSchema: dict[str, Any]
+    input_schema: dict[str, Any] = Field(..., alias='inputSchema')
     """A JSON Schema object defining the expected parameters for the tool."""
     model_config = ConfigDict(extra="allow")