fix: use strict=False for MCP tools to preserve optional params

MCP tools use standard JSON Schema conventions where optional params
are simply not in the required array. Setting strict=False for OpenAI
allows this to work properly, so the LLM won't be forced to provide
values for all parameters.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: cpsievert

chatlas/_tools.py

@@ -66,19 +66,26 @@ def __init__(
         description: str,
         parameters: dict[str, Any],
         annotations: "Optional[ToolAnnotations]" = None,
+        strict: Optional[bool] = None,
     ):
         self.name = name
         self.func = func
         self.annotations = annotations
         self._is_async = _utils.is_async_callable(func)
-        self.schema: "ChatCompletionToolParam" = {
-            "type": "function",
-            "function": {
-                "name": name,
-                "description": description,
-                "parameters": parameters,
-            },
+        func_schema: dict[str, Any] = {
+            "name": name,
+            "description": description,
+            "parameters": parameters,
         }
+        if strict is not None:
+            func_schema["strict"] = strict
+        self.schema: "ChatCompletionToolParam" = cast(
+            "ChatCompletionToolParam",
+            {
+                "type": "function",
+                "function": func_schema,
+            },
+        )
 
     @classmethod
     def from_func(
@@ -230,6 +237,9 @@ async def _call(**args: Any) -> AsyncGenerator[ContentToolResult, None]:
             description=mcp_tool.description or "",
             parameters=params,
             annotations=annotations,
+            # MCP tools use standard JSON Schema conventions for optional params
+            # (not in required array), which requires strict=False for OpenAI
+            strict=False,
         )
 
 
@@ -406,8 +416,6 @@ def sanitize_schema(
     - `title`: Pydantic includes titles at model/field level, but they're not needed
     - `format`: JSON Schema format hints (e.g., "uri", "date-time") that some
       providers like OpenAI reject
-    - `required`: OpenAI requires all properties to be in required array, with
-      optional params using anyOf with null type
     """
     if "title" in params:
         del params["title"]
@@ -416,28 +424,10 @@ def sanitize_schema(
         del params["format"]
 
     if "properties" in params and isinstance(params["properties"], dict):
-        required_keys = set(params.get("required", []))
-
-        for key, prop in params["properties"].items():
+        for prop in params["properties"].values():
             if isinstance(prop, dict):
                 sanitize_schema(prop)
 
-                # For optional properties (not in required), make them nullable
-                # OpenAI requires all props in required array, using anyOf with
-                # null type to indicate optionality
-                if key not in required_keys:
-                    prop_type = prop.get("type")
-                    if prop_type and prop_type != "null":
-                        # Convert to anyOf with null
-                        prop["anyOf"] = [{"type": prop_type}, {"type": "null"}]
-                        del prop["type"]
-                    elif "anyOf" not in prop and "oneOf" not in prop:
-                        # No type specified, just allow null
-                        prop["anyOf"] = [prop.copy(), {"type": "null"}]
-
-        # OpenAI requires all properties to be in required array
-        params["required"] = list(params["properties"].keys())
-
     return params