feat: allow users to add constraints and validators to ToolParam

protos/logical_plan/v1/tools.proto

@@ -6,6 +6,24 @@ import "logical_plan/v1/datatypes.proto";
 import "logical_plan/v1/complex_types.proto";
 import "logical_plan/v1/plans.proto";
 
+message NumericConstraint {
+  oneof kind {
+    sint32 int_value = 1;
+    float float_value = 2;
+  }
+}
+
+message ToolParameterConstraints {
+  optional NumericConstraint gt = 1;
+  optional NumericConstraint ge = 2;
+  optional NumericConstraint lt = 3;
+  optional NumericConstraint le = 4;
+  optional NumericConstraint multiple_of = 5;
+
+  optional uint32 min_length = 6;
+  optional uint32 max_length = 7;
+  optional string pattern = 8;
+}
 
 message ToolParameter {
   string name = 1;
@@ -15,6 +33,8 @@ message ToolParameter {
   bool has_default = 5;
   optional ScalarValue default_value = 6;
   repeated ScalarValue allowed_values = 7;
+  optional ToolParameterConstraints constraints = 8;
+  repeated string validator_names = 9;
 }
 
 message ToolDefinition {

src/fenic/_gen/protos/logical_plan/v1/tools_pb2.pyi

@@ -8,23 +8,55 @@ from typing import ClassVar as _ClassVar, Iterable as _Iterable, Mapping as _Map
 
 DESCRIPTOR: _descriptor.FileDescriptor
 
+class NumericConstraint(_message.Message):
+    __slots__ = ("int_value", "float_value")
+    INT_VALUE_FIELD_NUMBER: _ClassVar[int]
+    FLOAT_VALUE_FIELD_NUMBER: _ClassVar[int]
+    int_value: int
+    float_value: float
+    def __init__(self, int_value: _Optional[int] = ..., float_value: _Optional[float] = ...) -> None: ...
+
+class ToolParameterConstraints(_message.Message):
+    __slots__ = ("gt", "ge", "lt", "le", "multiple_of", "min_length", "max_length", "pattern")
+    GT_FIELD_NUMBER: _ClassVar[int]
+    GE_FIELD_NUMBER: _ClassVar[int]
+    LT_FIELD_NUMBER: _ClassVar[int]
+    LE_FIELD_NUMBER: _ClassVar[int]
+    MULTIPLE_OF_FIELD_NUMBER: _ClassVar[int]
+    MIN_LENGTH_FIELD_NUMBER: _ClassVar[int]
+    MAX_LENGTH_FIELD_NUMBER: _ClassVar[int]
+    PATTERN_FIELD_NUMBER: _ClassVar[int]
+    gt: NumericConstraint
+    ge: NumericConstraint
+    lt: NumericConstraint
+    le: NumericConstraint
+    multiple_of: NumericConstraint
+    min_length: int
+    max_length: int
+    pattern: str
+    def __init__(self, gt: _Optional[_Union[NumericConstraint, _Mapping]] = ..., ge: _Optional[_Union[NumericConstraint, _Mapping]] = ..., lt: _Optional[_Union[NumericConstraint, _Mapping]] = ..., le: _Optional[_Union[NumericConstraint, _Mapping]] = ..., multiple_of: _Optional[_Union[NumericConstraint, _Mapping]] = ..., min_length: _Optional[int] = ..., max_length: _Optional[int] = ..., pattern: _Optional[str] = ...) -> None: ...
+
 class ToolParameter(_message.Message):
-    __slots__ = ("name", "description", "data_type", "required", "has_default", "default_value", "allowed_values")
+    __slots__ = ("name", "description", "data_type", "required", "has_default", "default_value", "allowed_values", "constraints", "validator_names")
     NAME_FIELD_NUMBER: _ClassVar[int]
     DESCRIPTION_FIELD_NUMBER: _ClassVar[int]
     DATA_TYPE_FIELD_NUMBER: _ClassVar[int]
     REQUIRED_FIELD_NUMBER: _ClassVar[int]
     HAS_DEFAULT_FIELD_NUMBER: _ClassVar[int]
     DEFAULT_VALUE_FIELD_NUMBER: _ClassVar[int]
     ALLOWED_VALUES_FIELD_NUMBER: _ClassVar[int]
+    CONSTRAINTS_FIELD_NUMBER: _ClassVar[int]
+    VALIDATOR_NAMES_FIELD_NUMBER: _ClassVar[int]
     name: str
     description: str
     data_type: _datatypes_pb2.DataType
     required: bool
     has_default: bool
     default_value: _complex_types_pb2.ScalarValue
     allowed_values: _containers.RepeatedCompositeFieldContainer[_complex_types_pb2.ScalarValue]
-    def __init__(self, name: _Optional[str] = ..., description: _Optional[str] = ..., data_type: _Optional[_Union[_datatypes_pb2.DataType, _Mapping]] = ..., required: bool = ..., has_default: bool = ..., default_value: _Optional[_Union[_complex_types_pb2.ScalarValue, _Mapping]] = ..., allowed_values: _Optional[_Iterable[_Union[_complex_types_pb2.ScalarValue, _Mapping]]] = ...) -> None: ...
+    constraints: ToolParameterConstraints
+    validator_names: _containers.RepeatedScalarFieldContainer[str]
+    def __init__(self, name: _Optional[str] = ..., description: _Optional[str] = ..., data_type: _Optional[_Union[_datatypes_pb2.DataType, _Mapping]] = ..., required: bool = ..., has_default: bool = ..., default_value: _Optional[_Union[_complex_types_pb2.ScalarValue, _Mapping]] = ..., allowed_values: _Optional[_Iterable[_Union[_complex_types_pb2.ScalarValue, _Mapping]]] = ..., constraints: _Optional[_Union[ToolParameterConstraints, _Mapping]] = ..., validator_names: _Optional[_Iterable[str]] = ...) -> None: ...
 
 class ToolDefinition(_message.Message):
     __slots__ = ("name", "description", "params", "parameterized_view", "result_limit")

src/fenic/core/_serde/proto/serde_context.py

@@ -40,6 +40,7 @@
     FenicSchemaProto,
     LogicalExprProto,
     LogicalPlanProto,
+    NumericConstraintProto,
     NumpyArrayProto,
     ResolvedClassDefinitionProto,
     ResolvedModelAliasProto,
@@ -49,12 +50,18 @@
     ScalarStructProto,
     ScalarValueProto,
     ToolDefinitionProto,
+    ToolParameterConstraintsProto,
     ToolParameterProto,
 )
 from fenic.core._utils.structured_outputs import (
     check_if_model_uses_unserializable_features,
 )
-from fenic.core.mcp.types import BoundToolParam, UserDefinedTool
+from fenic.core.mcp._validators import get_param_validator
+from fenic.core.mcp.types import (
+    BoundToolParam,
+    ToolParamConstraints,
+    UserDefinedTool,
+)
 from fenic.core.types.datatypes import DataType
 from fenic.core.types.schema import ColumnField, Schema
 
@@ -884,6 +891,20 @@ def serialize_tool_parameter(
         """Serialize a ToolParameter."""
         with self.path_context(field_name):
             try:
+                c = tool_param.constraints
+                if c is not None:
+                    constraints = ToolParameterConstraintsProto(
+                        gt=_to_numeric_constraint(c.gt) if c.gt is not None else None,
+                        ge=_to_numeric_constraint(c.ge) if c.ge is not None else None,
+                        lt=_to_numeric_constraint(c.lt) if c.lt is not None else None,
+                        le=_to_numeric_constraint(c.le) if c.le is not None else None,
+                        multiple_of=_to_numeric_constraint(c.multiple_of) if c.multiple_of is not None else None,
+                        min_length=c.min_length,
+                        max_length=c.max_length,
+                        pattern=c.pattern,
+                    )
+                else:
+                    constraints = None
                 allowed_values = None
                 if tool_param.allowed_values:
                     allowed_values = [
@@ -898,6 +919,8 @@ def serialize_tool_parameter(
                     has_default=tool_param.has_default,
                     default_value=self.serialize_scalar_value("default_value", tool_param.default_value),
                     allowed_values=allowed_values,
+                    constraints=constraints,
+                    validator_names=[validator.name() for validator in tool_param.validators],
                 )
             except Exception as e:
                 self._handle_serde_error(e)
@@ -915,6 +938,20 @@ def deserialize_tool_parameter(
                     allowed_values = [
                         self.deserialize_scalar_value("allowed_values", allowed_value) for allowed_value in
                         tool_param_proto.allowed_values]
+
+                constraints = None
+                if tool_param_proto.constraints is not None:
+                    c = tool_param_proto.constraints
+                    constraints = ToolParamConstraints(
+                        gt=_from_numeric_constraint(c.gt) if c.HasField("gt") else None,
+                        ge=_from_numeric_constraint(c.ge) if c.HasField("ge") else None,
+                        lt=_from_numeric_constraint(c.lt) if c.HasField("lt") else None,
+                        le=_from_numeric_constraint(c.le) if c.HasField("le") else None,
+                        multiple_of=_from_numeric_constraint(c.multiple_of) if c.HasField("multiple_of") else None,
+                        min_length=c.min_length if c.HasField("min_length") else None,
+                        max_length=c.max_length if c.HasField("max_length") else None,
+                        pattern=c.pattern if c.HasField("pattern") else None,
+                    )
                 return BoundToolParam(
                     name=tool_param_proto.name,
                     description=tool_param_proto.description,
@@ -923,6 +960,8 @@ def deserialize_tool_parameter(
                     has_default=tool_param_proto.has_default,
                     default_value=self.deserialize_scalar_value("default_value", tool_param_proto.default_value),
                     allowed_values=allowed_values,
+                    constraints=constraints,
+                    validators=[get_param_validator(validator_name) for validator_name in tool_param_proto.validator_names],
                 )
             except Exception as e:
                 self._handle_serde_error(e)
@@ -1004,3 +1043,20 @@ def pop(self) -> None:
     def clear(self) -> None:
         """Clear the entire path stack."""
         self._path_stack.clear()
+
+def _to_numeric_constraint(value):
+    if isinstance(value, int):
+        return NumericConstraintProto(int_value=value)
+    if isinstance(value, float):
+        return NumericConstraintProto(float_value=value)
+    return None
+
+def _from_numeric_constraint(nc: Optional[NumericConstraintProto]):
+    if nc is None:
+        return None
+    which = nc.WhichOneof("kind")
+    if which == "int_value":
+        return nc.int_value
+    if which == "float_value":
+        return nc.float_value
+    return None

src/fenic/core/_serde/proto/types.py

@@ -574,12 +574,18 @@
 from fenic._gen.protos.logical_plan.v1.plans_pb2 import (
     Unnest as UnnestProto,
 )
+from fenic._gen.protos.logical_plan.v1.tools_pb2 import (
+    NumericConstraint as NumericConstraintProto,
+)
 from fenic._gen.protos.logical_plan.v1.tools_pb2 import (
     ToolDefinition as ToolDefinitionProto,
 )
 from fenic._gen.protos.logical_plan.v1.tools_pb2 import (
     ToolParameter as ToolParameterProto,
 )
+from fenic._gen.protos.logical_plan.v1.tools_pb2 import (
+    ToolParameterConstraints as ToolParameterConstraintsProto,
+)
 
 # Export all protobuf classes for easy importing
 __all__ = [
@@ -767,6 +773,9 @@
     # Tools
     "ToolParameterProto",
     "ToolDefinitionProto",
+    "ToolParameterConstraintsProto",
+    "NumericConstraintProto",
+    "ToolDefinitionProto",
     # Date time related classes
     "YearExprProto",
     "MonthExprProto",

src/fenic/core/mcp/_server.py

@@ -16,7 +16,7 @@
 from typing import Any, Callable, Coroutine, Dict, List, Optional, Union
 
 import polars as pl
-from pydantic import BaseModel, ConfigDict
+from pydantic import BaseModel, ConfigDict, Field
 from typing_extensions import Annotated, Literal
 
 from fenic.core._interfaces.session_state import BaseSessionState
@@ -37,6 +37,7 @@
 from fenic.core.mcp.types import (
     SystemTool,
     TableFormat,
+    ToolParamConstraints,
     UserDefinedTool,
 )
 from fenic.core.types.datatypes import ArrayType
@@ -216,28 +217,39 @@ async def tool_fn_wrapper(*args, **kwargs) -> MCPResultSet:
             # Add one keyword-only parameter per tool param
             for param in tool_definition.params:
                 param_type = _type_for_param(param)
-                param_annotation = _annotate_with_description(param_type, param.description)
                 default_value = param.default_value if param.has_default else inspect._empty
+                param_annotation = _annotate_with_description(param_type, param.description, param.constraints)
                 params.append(
                     inspect.Parameter(
                         name=param.name,
                         kind=inspect.Parameter.KEYWORD_ONLY,
-                        default=default_value,
                         annotation=param_annotation,
+                        default=default_value,
                     )
                 )
                 annotations[param.name] = param_annotation
 
             # Add table_format and limit just like system tools
-            tf_ann = Annotated[TableFormat, (
-                TABLE_FORMAT_DESCRIPTION
-            )]
-            lim_ann = Annotated[Optional[Union[str, int]], LIMIT_DESCRIPTION]
+            tf_ann = Annotated[
+                TableFormat,
+                Field(
+                    description=TABLE_FORMAT_DESCRIPTION,
+                    default="markdown"
+                )
+            ]
+            lim_ann = Annotated[
+                Optional[Union[str, int]],
+                Field(
+                    description=LIMIT_DESCRIPTION,
+                    gt=0,
+                    le=tool_definition.max_result_limit,
+                    default=tool_definition.max_result_limit
+                )
+            ]
             params.append(
                 inspect.Parameter(
                     name="table_format",
                     kind=inspect.Parameter.KEYWORD_ONLY,
-                    default="markdown",
                     annotation=tf_ann,
                 )
             )
@@ -384,10 +396,15 @@ def _type_for_param(p: BoundToolParam) -> type:
         base_py = Optional[base_py]
     return base_py
 
-def _annotate_with_description(base_ann: type, description: Optional[str] = None):
-    if description:
-        return Annotated[base_ann, description]
-    return base_ann
+def _annotate_with_description(
+    py_type: type,
+    description: Optional[str] = None,
+    constraints: Optional[ToolParamConstraints] = None
+) -> Union[type, Annotated[type, Field]]:
+    if description or constraints:
+        constraints_dict = constraints.model_dump() if constraints else {}
+        return Annotated[py_type, Field(description=description, **constraints_dict)]
+    return py_type
 
 def _render_markdown_preview(rows: List[Dict[str, Any]]) -> str:
     if not rows: