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Python: [Python] as_agent_framework_tool drops parameter defaults (optionals become required) #14481
Description
Description
KernelFunction.as_agent_framework_tool builds an agent-framework InputModel but drops parameter defaults. After assigning a Field(..., default=...) for optional params, the next line unconditionally overwrites the same key with a no-default Field, so every optional becomes required in the JSON schema.
Environment
semantic-kernel==1.44.1(Python)- Python 3.13
Minimal repro
The bug is in the field-building loop (exact code from as_agent_framework_tool):
from typing import Annotated
from pydantic import Field, create_model
from semantic_kernel.functions import KernelPlugin, kernel_function
@kernel_function(name="search", description="search things")
def search(
query: Annotated[str, "search query"],
top_k: Annotated[int, "number of results"] = 5,
include_meta: Annotated[bool, "include metadata"] = False,
) -> str:
return f"{query}:{top_k}:{include_meta}"
fn = KernelPlugin(name="S", functions=[search])["search"]
fields = {}
for param in fn.parameters:
if param.include_in_function_choices:
if param.default_value is not None:
fields[param.name] = (
param.type_,
Field(description=param.description, default=param.default_value),
)
fields[param.name] = (param.type_, Field(description=param.description)) # overwrites
Model = create_model("InputModel", **fields)
print(Model.model_json_schema().get("required"))
# ACTUAL: ['query', 'top_k', 'include_meta']
# EXPECTED: ['query'] (top_k / include_meta optional with defaults)(as_agent_framework_tool() itself also needs agent-framework-core; the loop above is the same code path.)
Expected
Optional kernel function parameters with defaults remain optional in the agent-framework InputModel / schema (top_k=5, include_meta=False).
Actual
All included params are required; defaults are discarded. Especially misleading for False/0 because default_value is not None is true, yet the default is still overwritten.
Root cause (pointer)
semantic_kernel/functions/kernel_function.py — as_agent_framework_tool (~field loop): missing else: around the no-default assignment.
Suggested fix direction
if param.default_value is not None:
fields[param.name] = (..., Field(..., default=param.default_value))
else:
fields[param.name] = (..., Field(...))(Also prefer param.type_object over the string param.type_ if available.)
Activity
[-][Python] as_agent_framework_tool drops parameter defaults (optionals become required)[/-][+]Python: [Python] as_agent_framework_tool drops parameter defaults (optionals become required)[/+]michaelkillgta commentedon Oct 15, 2026
Thanks — I see #14489 open for this, so I'll leave it there and won't open a competing PR.