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Python: fix(core): leave out description for MCP prompt arguments that have none #8733

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Merged
Eduard van Valkenburg (eavanvalkenburg) merged 1 commit into from
Sep 29, 2026
Merged

Python: fix(core): leave out description for MCP prompt arguments that have none #8733

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9 changes: 5 additions & 4 deletions python/packages/core/agent_framework/_mcp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -529,10 +529,11 @@ def _get_input_model_from_mcp_prompt(prompt: types.Prompt) -> dict[str, Any]:

for prompt_argument in prompt.arguments:
# For prompts, all arguments are typically string type unless specified otherwise
properties[prompt_argument.name] = {
"type": "string",
"description": prompt_argument.description if hasattr(prompt_argument, "description") else "",
}
# `description` is optional on PromptArgument and None when absent, which is not
# a valid JSON Schema description, so leave the key out instead.
properties[prompt_argument.name] = {"type": "string"}
if prompt_argument.description is not None:
properties[prompt_argument.name]["description"] = prompt_argument.description
if prompt_argument.required:
required.append(prompt_argument.name)

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15 changes: 15 additions & 0 deletions python/packages/core/tests/core/test_mcp.py
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Expand Up @@ -2203,6 +2203,21 @@ def test_get_input_model_from_mcp_prompt():
assert "arg2" not in result["required"]


def test_get_input_model_from_mcp_prompt_argument_without_description():
"""An argument with no description gets no description key, not `"description": None`."""
prompt = types.Prompt(
name="test_prompt",
arguments=[
types.PromptArgument(name="topic", required=True),
types.PromptArgument(name="tone", description="Tone of voice"),
],
)
result = _get_input_model_from_mcp_prompt(prompt)

assert result["properties"]["topic"] == {"type": "string"}
assert result["properties"]["tone"] == {"type": "string", "description": "Tone of voice"}


def test_get_input_model_from_mcp_prompt_without_arguments():
"""Test prompt schema generation when no prompt arguments are defined."""
prompt = types.Prompt(name="empty_prompt", description="No args prompt", arguments=[])
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