Description
- What happened? Agent called MCP server tool but response visible to the Agent was duplicated: one was content, the other was structuredContent. Occurred when using my own MCP server, but also tested on MS Learn MCP and Deep Wiki MCP servers.
- What I expected: no duplication, but structured content.
- Directly call MS Learn MCP / Deep Wiki MCP via call_tool and see results.
Code Sample
import asyncio
from agent_framework import MCPStreamableHTTPTool
# DeepWiki's server (built on fastmcp) tags each tool's `_meta` with a `_fastmcp`
# key, whose leading underscore violates the MCP spec's _meta key-name format.
# agent_framework enforces that format strictly and aborts tool loading over it,
# so relax it here to reach the server for this repro. Separate bug, unrelated
# to the duplicate-content issue below.
import agent_framework._mcp as _af_mcp
_af_mcp._validate_mcp_meta_key = lambda key: None
DEEPWIKI_MCP_URL = "https://mcp.deepwiki.com/mcp"
TOOL_NAME = "ask_question"
TOOL_ARGS = {"repoName": "microsoft/agent-framework", "question": "What is this repository about?"}
async def main() -> None:
async with MCPStreamableHTTPTool(name="DeepWiki", url=DEEPWIKI_MCP_URL, load_prompts=False) as deepwiki:
result = await deepwiki.call_tool(TOOL_NAME, **TOOL_ARGS)
print(f"call_tool() returned {len(result)} content item(s) (expected 1)")
for i, item in enumerate(result):
print(f" item[{i}]: {getattr(item, 'text', item)!r:.200}")
# Bypass agent_framework's parsing to inspect the raw CallToolResult:
# confirms the server sends exactly one `content` block plus
# `structuredContent` -- the duplication is manufactured client-side.
raw = await deepwiki.session.call_tool(TOOL_NAME, arguments=TOOL_ARGS)
print(f"raw.content: {len(raw.content)} block(s); raw.structuredContent is None: {raw.structuredContent is None}")
if __name__ == "__main__":
asyncio.run(main())Error Messages / Stack Traces
uv run python repro_mcp_duplicate_content.py
call_tool() returned 2 content item(s) (expected 1)
item[0]: 'This repository, `microsoft/agent-framework`, is a multi-language framework designed for building, orchestrating, and deploying AI agents . It provides parallel implementations in both .NET and Pytho
item[1]: '{"result": "This repository, `microsoft/agent-framework`, is a multi-language framework designed for building, orchestrating, and deploying AI agents . It provides parallel implementations in both .N
raw.content: 1 block(s); raw.structuredContent is None: FalsePackage Versions
1.13.0
Python Version
3.12
Additional Context
Probable root cause: agent_framework/_mcp.py::_parse_tool_result_from_mcp unconditionally
appends a second Content item built from structuredContent, even when content
already carries an equivalent serialization.
So even if for-loop succeeds appending content, next if block will append structuredContent anyway.
def _parse_tool_result_from_mcp(
self,
mcp_type: types.CallToolResult,
) -> list[Content]:
"""Parse an MCP CallToolResult into a list of Content items.
If the server attached a ``_meta`` payload to the tool result (e.g. for
Information Flow Control labels under the ``ifc`` key), a copy of that
payload is stamped onto each produced :class:`Content` instance under
``additional_properties["_meta"]``. Downstream layers (such as
:class:`agent_framework.security.SecureMCPToolProxy`) consume this key
to derive per-item security labels.
The sentinel is intentionally generic so any MCP server's ``_meta``
keys (current or future) can be interpreted by higher-level code.
"""
from mcp import types
raw_meta = mcp_type.meta
meta: dict[str, Any] | None = dict(raw_meta) if isinstance(raw_meta, Mapping) else None
# Stamp the server ``_meta`` payload directly via additional_properties on
# each newly constructed Content; empty when the server provided no meta.
additional_kwargs: dict[str, Any] = {"additional_properties": {"_meta": meta}} if meta else {}
result: list[Content] = []
for item in mcp_type.content:
match item:
case types.TextContent():
result.append(Content.from_text(item.text, **additional_kwargs))
case types.ImageContent() | types.AudioContent():
decoded = base64.b64decode(item.data)
result.append(
Content.from_data(
data=decoded,
media_type=item.mimeType,
**additional_kwargs,
)
)
case types.ResourceLink():
result.append(
Content.from_uri(
uri=str(item.uri),
media_type=item.mimeType,
**additional_kwargs,
)
)
case types.EmbeddedResource():
match item.resource:
case types.TextResourceContents():
result.append(Content.from_text(item.resource.text, **additional_kwargs))
case types.BlobResourceContents():
blob = item.resource.blob
mime = item.resource.mimeType or "application/octet-stream"
if not blob.startswith("data:"):
blob = f"data:{mime};base64,{blob}"
result.append(
Content.from_uri(
uri=blob,
media_type=mime,
**additional_kwargs,
)
)
case _:
result.append(Content.from_text(str(item), **additional_kwargs))
if mcp_type.structuredContent is not None:
result.append(Content.from_text(json.dumps(mcp_type.structuredContent, default=str)))
if not result:
result.append(Content.from_text("null", **additional_kwargs))
return result
Description
Code Sample
Error Messages / Stack Traces
Package Versions
1.13.0
Python Version
3.12
Additional Context
Probable root cause: agent_framework/_mcp.py::_parse_tool_result_from_mcp unconditionally
appends a second Content item built from
structuredContent, even whencontentalready carries an equivalent serialization.
So even if for-loop succeeds appending content, next if block will append structuredContent anyway.