Improve tool schema diagnostic errors

src/agents/function_schema.py

@@ -18,6 +18,14 @@
 from .strict_schema import ensure_strict_json_schema
 from .tool_context import ToolContext
 
+_PYDANTIC_PROTECTED_FIELD_NAMES = {
+    "model_dump",
+    "model_dump_json",
+    "model_validate",
+    "model_validate_json",
+    "model_validate_strings",
+}
+
 
 @dataclass
 class FuncSchema:
@@ -319,6 +327,12 @@ def function_schema(
     fields: dict[str, Any] = {}
 
     for name, param in filtered_params:
+        if name in _PYDANTIC_PROTECTED_FIELD_NAMES:
+            raise UserError(
+                f"Function parameter {name!r} conflicts with a reserved Pydantic BaseModel "
+                "method name. Rename the parameter before using it as a function tool."
+            )
+
         ann = type_hints.get(name, param.annotation)
         default = param.default
 

src/agents/strict_schema.py

@@ -156,7 +156,10 @@ def resolve_ref(*, root: dict[str, object], ref: str) -> object:
     path = ref[2:].split("/")
     resolved = root
     for key in path:
-        value = resolved[key]
+        try:
+            value = resolved[key]
+        except KeyError as exc:
+            raise ValueError(f"Unable to resolve $ref {ref!r}: missing key {key!r}") from exc
         assert is_dict(value), (
             f"encountered non-dictionary entry while resolving {ref} - {resolved}"
         )

tests/test_function_schema.py

@@ -399,6 +399,25 @@ def func(a: int, context: RunContextWrapper) -> None:
         function_schema(func, use_docstring_info=False)
 
 
+@pytest.mark.parametrize(
+    "param_name",
+    [
+        "model_dump",
+        "model_dump_json",
+        "model_validate",
+        "model_validate_json",
+        "model_validate_strings",
+    ],
+)
+def test_pydantic_protected_parameter_names_raise_user_error(param_name: str) -> None:
+    code = f"def protected_param({param_name}: str, query: str) -> str:\n    return query"
+    namespace: dict[str, Any] = {}
+    exec(code, namespace)
+
+    with pytest.raises(UserError, match=f"Function parameter '{param_name}' conflicts"):
+        function_schema(namespace["protected_param"], use_docstring_info=False)
+
+
 def test_var_positional_tuple_annotation():
     # When a function has a var-positional parameter annotated with a tuple type,
     # function_schema() should convert it into a field with type List[<tuple-element>].

tests/test_strict_schema.py

@@ -145,6 +145,20 @@ def test_invalid_ref_format():
         ensure_strict_json_schema(schema)
 
 
+def test_missing_ref_path_raises_clear_value_error():
+    schema = {
+        "type": "object",
+        "properties": {
+            "data": {"$ref": "#/$defs/SomeType", "description": "desc"},
+        },
+    }
+
+    with pytest.raises(
+        ValueError, match=r"Unable to resolve \$ref '#/\$defs/SomeType': missing key '\$defs'"
+    ):
+        ensure_strict_json_schema(schema)
+
+
 def test_chained_ref_with_sibling_keys_is_resolved():
     # When a $ref points to a definition that is itself just a $ref (a chained alias),
     # and the original $ref has sibling keys (like "description"), the chain must be