Merge pull request #31 from jurasofish/draft-handling-of-complex-inputs

README.md

@@ -212,6 +212,27 @@ async def fetch_weather(city: str) -> str:
         return response.text
 ```
 
+Complex input handling example:
+```python
+from pydantic import BaseModel, Field
+from typing import Annotated
+
+class ShrimpTank(BaseModel):
+    class Shrimp(BaseModel):
+        name: Annotated[str, Field(max_length=10)]
+
+    shrimp: list[Shrimp]
+
+@mcp.tool()
+def name_shrimp(
+    tank: ShrimpTank,
+    # You can use pydantic Field in function signatures for validation.
+    extra_names: Annotated[list[str], Field(max_length=10)],
+) -> list[str]:
+    """List all shrimp names in the tank"""
+    return [shrimp.name for shrimp in tank.shrimp] + extra_names
+```
+
 ### Prompts
 
 Prompts are reusable templates that help LLMs interact with your server effectively. They're like "best practices" encoded into your server. A prompt can be as simple as a string:

examples/complex_inputs.py

@@ -0,0 +1,28 @@
+"""
+FastMCP Complex inputs Example
+
+Demonstrates validation via pydantic with complex models.
+"""
+
+from pydantic import BaseModel, Field
+from typing import Annotated
+from fastmcp.server import FastMCP
+
+mcp = FastMCP("Shrimp Tank")
+
+
+class ShrimpTank(BaseModel):
+    class Shrimp(BaseModel):
+        name: Annotated[str, Field(max_length=10)]
+
+    shrimp: list[Shrimp]
+
+
+@mcp.tool()
+def name_shrimp(
+    tank: ShrimpTank,
+    # You can use pydantic Field in function signatures for validation.
+    extra_names: Annotated[list[str], Field(max_length=10)],
+) -> list[str]:
+    """List all shrimp names in the tank"""
+    return [shrimp.name for shrimp in tank.shrimp] + extra_names

src/fastmcp/exceptions.py

@@ -15,3 +15,7 @@ class ResourceError(FastMCPError):
 
 class ToolError(FastMCPError):
     """Error in tool operations."""
+
+
+class InvalidSignature(Exception):
+    """Invalid signature for use with FastMCP."""

src/fastmcp/tools/base.py

@@ -1,8 +1,8 @@
 import fastmcp
 from fastmcp.exceptions import ToolError
 
-
-from pydantic import BaseModel, Field, TypeAdapter, validate_call
+from fastmcp.utilities.func_metadata import func_metadata, FuncMetadata
+from pydantic import BaseModel, Field
 
 
 import inspect
@@ -19,6 +19,9 @@ class Tool(BaseModel):
     name: str = Field(description="Name of the tool")
     description: str = Field(description="Description of what the tool does")
     parameters: dict = Field(description="JSON schema for tool parameters")
+    fn_metadata: FuncMetadata = Field(
+        description="Metadata about the function including a pydantic model for tool arguments"
+    )
     is_async: bool = Field(description="Whether the tool is async")
     context_kwarg: Optional[str] = Field(
         None, description="Name of the kwarg that should receive context"
@@ -41,9 +44,6 @@ class Tool(BaseModel):
         func_doc = description or fn.__doc__ or ""
         is_async = inspect.iscoroutinefunction(fn)
 
-        # Get schema from TypeAdapter - will fail if function isn't properly typed
-        parameters = TypeAdapter(fn).json_schema()
-
         # Find context parameter if it exists
         if context_kwarg is None:
             sig = inspect.signature(fn)
@@ -52,14 +52,18 @@ class Tool(BaseModel):
                     context_kwarg = param_name
                     break
 
-        # ensure the arguments are properly cast
-        fn = validate_call(fn)
+        func_arg_metadata = func_metadata(
+            fn,
+            skip_names=[context_kwarg] if context_kwarg is not None else [],
+        )
+        parameters = func_arg_metadata.arg_model.model_json_schema()
 
         return cls(
             fn=fn,
             name=func_name,
             description=func_doc,
             parameters=parameters,
+            fn_metadata=func_arg_metadata,
             is_async=is_async,
             context_kwarg=context_kwarg,
         )
@@ -67,13 +71,13 @@ class Tool(BaseModel):
     async def run(self, arguments: dict, context: Optional["Context"] = None) -> Any:
         """Run the tool with arguments."""
         try:
-            # Inject context if needed
-            if self.context_kwarg:
-                arguments[self.context_kwarg] = context
-
-            # Call function with proper async handling
-            if self.is_async:
-                return await self.fn(**arguments)
-            return self.fn(**arguments)
+            return await self.fn_metadata.call_fn_with_arg_validation(
+                self.fn,
+                self.is_async,
+                arguments,
+                {self.context_kwarg: context}
+                if self.context_kwarg is not None
+                else None,
+            )
         except Exception as e:
             raise ToolError(f"Error executing tool {self.name}: {e}") from e

src/fastmcp/utilities/func_metadata.py

@@ -0,0 +1,200 @@
+import inspect
+from collections.abc import Callable, Sequence, Awaitable
+from typing import (
+    Annotated,
+    Any,
+    Dict,
+    ForwardRef,
+)
+from pydantic import Field
+from fastmcp.exceptions import InvalidSignature
+from pydantic._internal._typing_extra import try_eval_type
+import json
+from pydantic import BaseModel
+from pydantic.fields import FieldInfo
+from pydantic import ConfigDict, create_model
+from pydantic import WithJsonSchema
+from pydantic_core import PydanticUndefined
+from fastmcp.utilities.logging import get_logger
+
+
+logger = get_logger(__name__)
+
+
+class ArgModelBase(BaseModel):
+    """A model representing the arguments to a function."""
+
+    def model_dump_one_level(self) -> dict[str, Any]:
+        """Return a dict of the model's fields, one level deep.
+
+        That is, sub-models etc are not dumped - they are kept as pydantic models.
+        """
+        kwargs: dict[str, Any] = {}
+        for field_name in self.model_fields.keys():
+            kwargs[field_name] = getattr(self, field_name)
+        return kwargs
+
+    model_config = ConfigDict(
+        arbitrary_types_allowed=True,
+    )
+
+
+class FuncMetadata(BaseModel):
+    arg_model: Annotated[type[ArgModelBase], WithJsonSchema(None)]
+    # We can add things in the future like
+    #  - Maybe some args are excluded from attempting to parse from JSON
+    #  - Maybe some args are special (like context) for dependency injection
+
+    async def call_fn_with_arg_validation(
+        self,
+        fn: Callable | Awaitable,
+        fn_is_async: bool,
+        arguments_to_validate: dict[str, Any],
+        arguments_to_pass_directly: dict[str, Any] | None,
+    ) -> Any:
+        """Call the given function with arguments validated and injected.
+
+        Arguments are first attempted to be parsed from JSON, then validated against
+        the argument model, before being passed to the function.
+        """
+        arguments_pre_parsed = self.pre_parse_json(arguments_to_validate)
+        arguments_parsed_model = self.arg_model.model_validate(arguments_pre_parsed)
+        arguments_parsed_dict = arguments_parsed_model.model_dump_one_level()
+
+        arguments_parsed_dict |= arguments_to_pass_directly or {}
+
+        if fn_is_async:
+            return await fn(**arguments_parsed_dict)
+        return fn(**arguments_parsed_dict)
+
+    def pre_parse_json(self, data: dict[str, Any]) -> dict[str, Any]:
+        """Pre-parse data from JSON.
+
+        Return a dict with same keys as input but with values parsed from JSON
+        if appropriate.
+
+        This is to handle cases like `["a", "b", "c"]` being passed in as JSON inside
+        a string rather than an actual list. Claude desktop is prone to this - in fact
+        it seems incapable of NOT doing this. For sub-models, it tends to pass
+        dicts (JSON objects) as JSON strings, which can be pre-parsed here.
+        """
+        new_data = data.copy()  # Shallow copy
+        for field_name, field_info in self.arg_model.model_fields.items():
+            if field_name not in data.keys():
+                continue
+            if isinstance(data[field_name], str):
+                try:
+                    pre_parsed = json.loads(data[field_name])
+                except json.JSONDecodeError:
+                    continue  # Not JSON - skip
+                if isinstance(pre_parsed, str):
+                    # This is likely that the raw value is e.g. `"hello"` which we
+                    # Should really be parsed as '"hello"' in Python - but if we parse
+                    # it as JSON it'll turn into just 'hello'. So we skip it.
+                    continue
+                new_data[field_name] = pre_parsed
+        assert new_data.keys() == data.keys()
+        return new_data
+
+    model_config = ConfigDict(
+        arbitrary_types_allowed=True,
+    )
+
+
+def func_metadata(func: Callable, skip_names: Sequence[str] = ()) -> FuncMetadata:
+    """Given a function, return metadata including a pydantic model representing its signature.
+
+    The use case for this is
+    ```
+    meta = func_to_pyd(func)
+    validated_args = meta.arg_model.model_validate(some_raw_data_dict)
+    return func(**validated_args.model_dump_one_level())
+    ```
+
+    **critically** it also provides pre-parse helper to attempt to parse things from JSON.
+
+    Args:
+        func: The function to convert to a pydantic model
+        skip_names: A list of parameter names to skip. These will not be included in
+            the model.
+    Returns:
+        A pydantic model representing the function's signature.
+    """
+    sig = _get_typed_signature(func)
+    params = sig.parameters
+    dynamic_pydantic_model_params: dict[str, Any] = {}
+    for param in params.values():
+        if param.name.startswith("_"):
+            raise InvalidSignature(
+                f"Parameter {param.name} of {func.__name__} may not start with an underscore"
+            )
+        if param.name in skip_names:
+            continue
+        annotation = param.annotation
+
+        # `x: None` / `x: None = None`
+        if annotation is None:
+            annotation = Annotated[
+                None,
+                Field(
+                    default=param.default
+                    if param.default is not inspect.Parameter.empty
+                    else PydanticUndefined
+                ),
+            ]
+
+        # Untyped field
+        if annotation is inspect.Parameter.empty:
+            annotation = Annotated[
+                Any,
+                Field(),
+                # 🤷
+                WithJsonSchema({"title": param.name, "type": "string"}),
+            ]
+
+        field_info = FieldInfo.from_annotated_attribute(
+            annotation,
+            param.default
+            if param.default is not inspect.Parameter.empty
+            else PydanticUndefined,
+        )
+        dynamic_pydantic_model_params[param.name] = (field_info.annotation, field_info)
+        continue
+
+    arguments_model = create_model(
+        f"{func.__name__}Arguments",
+        **dynamic_pydantic_model_params,
+        __base__=ArgModelBase,
+    )
+    resp = FuncMetadata(arg_model=arguments_model)
+    return resp
+
+
+def _get_typed_annotation(annotation: Any, globalns: Dict[str, Any]) -> Any:
+    if isinstance(annotation, str):
+        annotation = ForwardRef(annotation)
+        annotation, status = try_eval_type(annotation, globalns, globalns)
+
+        # This check and raise could perhaps be skipped, and we (FastMCP) just call
+        # model_rebuild right before using it 🤷
+        if status is False:
+            raise InvalidSignature(f"Unable to evaluate type annotation {annotation}")
+
+    return annotation
+
+
+def _get_typed_signature(call: Callable[..., Any]) -> inspect.Signature:
+    """Get function signature while evaluating forward references"""
+    signature = inspect.signature(call)
+    globalns = getattr(call, "__globals__", {})
+    typed_params = [
+        inspect.Parameter(
+            name=param.name,
+            kind=param.kind,
+            default=param.default,
+            annotation=_get_typed_annotation(param.annotation, globalns),
+        )
+        for param in signature.parameters.values()
+    ]
+    typed_signature = inspect.Signature(typed_params)
+    return typed_signature

tests/test_func_metadata.py

@@ -0,0 +1,359 @@
+from pydantic import BaseModel, Field
+from typing import Annotated
+import annotated_types
+from fastmcp.utilities.func_metadata import func_metadata
+import pytest
+
+
+class TestInputModelA(BaseModel):
+    pass
+
+
+class TestInputModelB(BaseModel):
+    class InnerModel(BaseModel):
+        x: int
+
+    how_many_shrimp: Annotated[int, Field(description="How many shrimp in the tank???")]
+    ok: InnerModel
+    y: None
+
+
+def complex_arguments_fn(
+    an_int: int,
+    must_be_none: None,
+    must_be_none_dumb_annotation: Annotated[None, "blah"],
+    list_of_ints: list[int],
+    # list[str] | str is an interesting case because if it comes in as JSON like
+    # "[\"a\", \"b\"]" then it will be naively parsed as a string.
+    list_str_or_str: list[str] | str,
+    an_int_annotated_with_field: Annotated[
+        int, Field(description="An int with a field")
+    ],
+    an_int_annotated_with_field_and_others: Annotated[
+        int,
+        str,  # Should be ignored, really
+        Field(description="An int with a field"),
+        annotated_types.Gt(1),
+    ],
+    an_int_annotated_with_junk: Annotated[
+        int,
+        "123",
+        456,
+    ],
+    field_with_default_via_field_annotation_before_nondefault_arg: Annotated[
+        int, Field(1)
+    ],
+    unannotated,
+    my_model_a: TestInputModelA,
+    my_model_a_forward_ref: "TestInputModelA",
+    my_model_b: TestInputModelB,
+    an_int_annotated_with_field_default: Annotated[
+        int,
+        Field(1, description="An int with a field"),
+    ],
+    unannotated_with_default=5,
+    my_model_a_with_default: TestInputModelA = TestInputModelA(),  # noqa: B008
+    an_int_with_default: int = 1,
+    must_be_none_with_default: None = None,
+    an_int_with_equals_field: int = Field(1, ge=0),
+    int_annotated_with_default: Annotated[int, Field(description="hey")] = 5,
+) -> str:
+    _ = (
+        an_int,
+        must_be_none,
+        must_be_none_dumb_annotation,
+        list_of_ints,
+        list_str_or_str,
+        an_int_annotated_with_field,
+        an_int_annotated_with_field_and_others,
+        an_int_annotated_with_junk,
+        field_with_default_via_field_annotation_before_nondefault_arg,
+        unannotated,
+        an_int_annotated_with_field_default,
+        unannotated_with_default,
+        my_model_a,
+        my_model_a_forward_ref,
+        my_model_b,
+        my_model_a_with_default,
+        an_int_with_default,
+        must_be_none_with_default,
+        an_int_with_equals_field,
+        int_annotated_with_default,
+    )
+    return "ok!"
+
+
+async def test_complex_function_runtime_arg_validation_non_json():
+    """Test that basic non-JSON arguments are validated correctly"""
+    meta = func_metadata(complex_arguments_fn)
+
+    # Test with minimum required arguments
+    result = await meta.call_fn_with_arg_validation(
+        complex_arguments_fn,
+        fn_is_async=False,
+        arguments_to_validate={
+            "an_int": 1,
+            "must_be_none": None,
+            "must_be_none_dumb_annotation": None,
+            "list_of_ints": [1, 2, 3],
+            "list_str_or_str": "hello",
+            "an_int_annotated_with_field": 42,
+            "an_int_annotated_with_field_and_others": 5,
+            "an_int_annotated_with_junk": 100,
+            "unannotated": "test",
+            "my_model_a": {},
+            "my_model_a_forward_ref": {},
+            "my_model_b": {"how_many_shrimp": 5, "ok": {"x": 1}, "y": None},
+        },
+        arguments_to_pass_directly=None,
+    )
+    assert result == "ok!"
+
+    # Test with invalid types
+    with pytest.raises(ValueError):
+        await meta.call_fn_with_arg_validation(
+            complex_arguments_fn,
+            fn_is_async=False,
+            arguments_to_validate={"an_int": "not an int"},
+            arguments_to_pass_directly=None,
+        )
+
+
+async def test_complex_function_runtime_arg_validation_with_json():
+    """Test that JSON string arguments are parsed and validated correctly"""
+    meta = func_metadata(complex_arguments_fn)
+
+    result = await meta.call_fn_with_arg_validation(
+        complex_arguments_fn,
+        fn_is_async=False,
+        arguments_to_validate={
+            "an_int": 1,
+            "must_be_none": None,
+            "must_be_none_dumb_annotation": None,
+            "list_of_ints": "[1, 2, 3]",  # JSON string
+            "list_str_or_str": '["a", "b", "c"]',  # JSON string
+            "an_int_annotated_with_field": 42,
+            "an_int_annotated_with_field_and_others": "5",  # JSON string
+            "an_int_annotated_with_junk": 100,
+            "unannotated": "test",
+            "my_model_a": "{}",  # JSON string
+            "my_model_a_forward_ref": "{}",  # JSON string
+            "my_model_b": '{"how_many_shrimp": 5, "ok": {"x": 1}, "y": null}',  # JSON string
+        },
+        arguments_to_pass_directly=None,
+    )
+    assert result == "ok!"
+
+
+def test_str_vs_list_str():
+    """Test handling of string vs list[str] type annotations.
+
+    This is tricky as '"hello"' can be parsed as a JSON string or a Python string.
+    We want to make sure it's kept as a python string.
+    """
+
+    def func_with_str_types(str_or_list: str | list[str]):
+        return str_or_list
+
+    meta = func_metadata(func_with_str_types)
+
+    # Test string input for union type
+    result = meta.pre_parse_json({"str_or_list": "hello"})
+    assert result["str_or_list"] == "hello"
+
+    # Test string input that contains valid JSON for union type
+    # We want to see here that the JSON-vali string is NOT parsed as JSON, but rather
+    # kept as a raw string
+    result = meta.pre_parse_json({"str_or_list": '"hello"'})
+    assert result["str_or_list"] == '"hello"'
+
+    # Test list input for union type
+    result = meta.pre_parse_json({"str_or_list": '["hello", "world"]'})
+    assert result["str_or_list"] == ["hello", "world"]
+
+
+def test_skip_names():
+    """Test that skipped parameters are not included in the model"""
+
+    def func_with_many_params(
+        keep_this: int, skip_this: str, also_keep: float, also_skip: bool
+    ):
+        return keep_this, skip_this, also_keep, also_skip
+
+    # Skip some parameters
+    meta = func_metadata(func_with_many_params, skip_names=["skip_this", "also_skip"])
+
+    # Check model fields
+    assert "keep_this" in meta.arg_model.model_fields
+    assert "also_keep" in meta.arg_model.model_fields
+    assert "skip_this" not in meta.arg_model.model_fields
+    assert "also_skip" not in meta.arg_model.model_fields
+
+    # Validate that we can call with only non-skipped parameters
+    model = meta.arg_model.model_validate({"keep_this": 1, "also_keep": 2.5})
+    assert model.keep_this == 1
+    assert model.also_keep == 2.5
+
+
+async def test_lambda_function():
+    """Test lambda function schema and validation"""
+    fn = lambda x, y=5: x  # noqa: E731
+    meta = func_metadata(lambda x, y=5: x)
+
+    # Test schema
+    assert meta.arg_model.model_json_schema() == {
+        "properties": {
+            "x": {"title": "x", "type": "string"},
+            "y": {"default": 5, "title": "y", "type": "string"},
+        },
+        "required": ["x"],
+        "title": "<lambda>Arguments",
+        "type": "object",
+    }
+
+    async def check_call(args):
+        return await meta.call_fn_with_arg_validation(
+            fn,
+            fn_is_async=False,
+            arguments_to_validate=args,
+            arguments_to_pass_directly=None,
+        )
+
+    # Basic calls
+    assert await check_call({"x": "hello"}) == "hello"
+    assert await check_call({"x": "hello", "y": "world"}) == "hello"
+    assert await check_call({"x": '"hello"'}) == '"hello"'
+
+    # Missing required arg
+    with pytest.raises(ValueError):
+        await check_call({"y": "world"})
+
+
+def test_complex_function_json_schema():
+    meta = func_metadata(complex_arguments_fn)
+    assert meta.arg_model.model_json_schema() == {
+        "$defs": {
+            "InnerModel": {
+                "properties": {"x": {"title": "X", "type": "integer"}},
+                "required": ["x"],
+                "title": "InnerModel",
+                "type": "object",
+            },
+            "TestInputModelA": {
+                "properties": {},
+                "title": "TestInputModelA",
+                "type": "object",
+            },
+            "TestInputModelB": {
+                "properties": {
+                    "how_many_shrimp": {
+                        "description": "How many shrimp in the tank???",
+                        "title": "How Many Shrimp",
+                        "type": "integer",
+                    },
+                    "ok": {"$ref": "#/$defs/InnerModel"},
+                    "y": {"title": "Y", "type": "null"},
+                },
+                "required": ["how_many_shrimp", "ok", "y"],
+                "title": "TestInputModelB",
+                "type": "object",
+            },
+        },
+        "properties": {
+            "an_int": {"title": "An Int", "type": "integer"},
+            "must_be_none": {"title": "Must Be None", "type": "null"},
+            "must_be_none_dumb_annotation": {
+                "title": "Must Be None Dumb Annotation",
+                "type": "null",
+            },
+            "list_of_ints": {
+                "items": {"type": "integer"},
+                "title": "List Of Ints",
+                "type": "array",
+            },
+            "list_str_or_str": {
+                "anyOf": [
+                    {"items": {"type": "string"}, "type": "array"},
+                    {"type": "string"},
+                ],
+                "title": "List Str Or Str",
+            },
+            "an_int_annotated_with_field": {
+                "description": "An int with a field",
+                "title": "An Int Annotated With Field",
+                "type": "integer",
+            },
+            "an_int_annotated_with_field_and_others": {
+                "description": "An int with a field",
+                "exclusiveMinimum": 1,
+                "title": "An Int Annotated With Field And Others",
+                "type": "integer",
+            },
+            "an_int_annotated_with_junk": {
+                "title": "An Int Annotated With Junk",
+                "type": "integer",
+            },
+            "field_with_default_via_field_annotation_before_nondefault_arg": {
+                "default": 1,
+                "title": "Field With Default Via Field Annotation Before Nondefault Arg",
+                "type": "integer",
+            },
+            "unannotated": {"title": "unannotated", "type": "string"},
+            "my_model_a": {"$ref": "#/$defs/TestInputModelA"},
+            "my_model_a_forward_ref": {"$ref": "#/$defs/TestInputModelA"},
+            "my_model_b": {"$ref": "#/$defs/TestInputModelB"},
+            "an_int_annotated_with_field_default": {
+                "default": 1,
+                "description": "An int with a field",
+                "title": "An Int Annotated With Field Default",
+                "type": "integer",
+            },
+            "unannotated_with_default": {
+                "default": 5,
+                "title": "unannotated_with_default",
+                "type": "string",
+            },
+            "my_model_a_with_default": {
+                "$ref": "#/$defs/TestInputModelA",
+                "default": {},
+            },
+            "an_int_with_default": {
+                "default": 1,
+                "title": "An Int With Default",
+                "type": "integer",
+            },
+            "must_be_none_with_default": {
+                "default": None,
+                "title": "Must Be None With Default",
+                "type": "null",
+            },
+            "an_int_with_equals_field": {
+                "default": 1,
+                "minimum": 0,
+                "title": "An Int With Equals Field",
+                "type": "integer",
+            },
+            "int_annotated_with_default": {
+                "default": 5,
+                "description": "hey",
+                "title": "Int Annotated With Default",
+                "type": "integer",
+            },
+        },
+        "required": [
+            "an_int",
+            "must_be_none",
+            "must_be_none_dumb_annotation",
+            "list_of_ints",
+            "list_str_or_str",
+            "an_int_annotated_with_field",
+            "an_int_annotated_with_field_and_others",
+            "an_int_annotated_with_junk",
+            "unannotated",
+            "my_model_a",
+            "my_model_a_forward_ref",
+            "my_model_b",
+        ],
+        "title": "complex_arguments_fnArguments",
+        "type": "object",
+    }

tests/test_tool_manager.py

@@ -3,7 +3,7 @@ from typing import Optional
 
 import pytest
 from pydantic import BaseModel
-
+import json
 from fastmcp.exceptions import ToolError
 from fastmcp.tools import ToolManager
 
@@ -156,6 +156,74 @@ class TestCallTools:
         with pytest.raises(ToolError):
             await manager.call_tool("unknown", {"a": 1})
 
+    async def test_call_tool_with_list_int_input(self):
+        def sum_vals(vals: list[int]) -> int:
+            return sum(vals)
+
+        manager = ToolManager()
+        manager.add_tool(sum_vals)
+        # Try both with plain list and with JSON list
+        result = await manager.call_tool("sum_vals", {"vals": "[1, 2, 3]"})
+        assert result == 6
+        result = await manager.call_tool("sum_vals", {"vals": [1, 2, 3]})
+        assert result == 6
+
+    async def test_call_tool_with_list_str_or_str_input(self):
+        def concat_strs(vals: list[str] | str) -> str:
+            return vals if isinstance(vals, str) else "".join(vals)
+
+        manager = ToolManager()
+        manager.add_tool(concat_strs)
+        # Try both with plain python object and with JSON list
+        result = await manager.call_tool("concat_strs", {"vals": ["a", "b", "c"]})
+        assert result == "abc"
+        result = await manager.call_tool("concat_strs", {"vals": '["a", "b", "c"]'})
+        assert result == "abc"
+        result = await manager.call_tool("concat_strs", {"vals": "a"})
+        assert result == "a"
+        result = await manager.call_tool("concat_strs", {"vals": '"a"'})
+        assert result == '"a"'
+
+    async def test_call_tool_with_complex_model(self):
+        from fastmcp import Context
+
+        class MyShrimpTank(BaseModel):
+            class Shrimp(BaseModel):
+                name: str
+
+            shrimp: list[Shrimp]
+            x: None
+
+        def name_shrimp(tank: MyShrimpTank, ctx: Context) -> list[str]:
+            return [x.name for x in tank.shrimp]
+
+        manager = ToolManager()
+        manager.add_tool(name_shrimp)
+        result = await manager.call_tool(
+            "name_shrimp",
+            {"tank": {"x": None, "shrimp": [{"name": "rex"}, {"name": "gertrude"}]}},
+        )
+        assert result == ["rex", "gertrude"]
+        result = await manager.call_tool(
+            "name_shrimp",
+            {"tank": '{"x": null, "shrimp": [{"name": "rex"}, {"name": "gertrude"}]}'},
+        )
+        assert result == ["rex", "gertrude"]
+
+
+class TestToolSchema:
+    async def test_context_arg_excluded_from_schema(self):
+        from fastmcp import Context
+
+        def something(a: int, ctx: Context) -> int:
+            return a
+
+        manager = ToolManager()
+        tool = manager.add_tool(something)
+        assert "ctx" not in json.dumps(tool.parameters)
+        assert "Context" not in json.dumps(tool.parameters)
+        assert "ctx" not in tool.fn_metadata.arg_model.model_fields
+
 
 class TestContextHandling:
     """Test context handling in the tool manager."""