fix(tool/decorator): validate ToolContext parameter name and raise clear error (#1028)

Author: Ratish1

src/strands/tools/decorator.py

@@ -99,6 +99,8 @@ def __init__(self, func: Callable[..., Any], context_param: str | None = None) -
         self.type_hints = get_type_hints(func)
         self._context_param = context_param
 
+        self._validate_signature()
+
         # Parse the docstring with docstring_parser
         doc_str = inspect.getdoc(func) or ""
         self.doc = docstring_parser.parse(doc_str)
@@ -111,6 +113,20 @@ def __init__(self, func: Callable[..., Any], context_param: str | None = None) -
         # Create a Pydantic model for validation
         self.input_model = self._create_input_model()
 
+    def _validate_signature(self) -> None:
+        """Verify that ToolContext is used correctly in the function signature."""
+        for param in self.signature.parameters.values():
+            if param.annotation is ToolContext:
+                if self._context_param is None:
+                    raise ValueError("@tool(context) must be set if passing in ToolContext param")
+
+                if param.name != self._context_param:
+                    raise ValueError(
+                        f"param_name=<{param.name}> | ToolContext param must be named '{self._context_param}'"
+                    )
+                # Found the parameter, no need to check further
+                break
+
     def _create_input_model(self) -> Type[BaseModel]:
         """Create a Pydantic model from function signature for input validation.
 

tests/strands/tools/test_decorator.py

@@ -1363,3 +1363,27 @@ async def async_generator() -> AsyncGenerator:
     ]
 
     assert act_results == exp_results
+
+
+def test_function_tool_metadata_validate_signature_default_context_name_mismatch():
+    with pytest.raises(ValueError, match=r"param_name=<context> | ToolContext param must be named 'tool_context'"):
+
+        @strands.tool(context=True)
+        def my_tool(context: ToolContext):
+            pass
+
+
+def test_function_tool_metadata_validate_signature_custom_context_name_mismatch():
+    with pytest.raises(ValueError, match=r"param_name=<tool_context> | ToolContext param must be named 'my_context'"):
+
+        @strands.tool(context="my_context")
+        def my_tool(tool_context: ToolContext):
+            pass
+
+
+def test_function_tool_metadata_validate_signature_missing_context_config():
+    with pytest.raises(ValueError, match=r"@tool\(context\) must be set if passing in ToolContext param"):
+
+        @strands.tool
+        def my_tool(tool_context: ToolContext):
+            pass