fix: propagate is_error flag from SDK MCP tool results#568
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Jbermingham1 wants to merge 1 commit intoanthropics:mainfrom
Open
fix: propagate is_error flag from SDK MCP tool results#568Jbermingham1 wants to merge 1 commit intoanthropics:mainfrom
Jbermingham1 wants to merge 1 commit intoanthropics:mainfrom
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The call_tool handler in create_sdk_mcp_server discards the is_error
flag from tool return values, always producing CallToolResult(isError=False).
This contradicts the documented API (lines 133-140) which shows tools
returning {"is_error": True} to indicate errors.
Fix: when is_error is True, raise ValueError with the error text so
the MCP decorator catches it and wraps in CallToolResult(isError=True),
matching the existing exception-based error path.
Closes anthropics#564
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Summary
Fixes #564 — the
is_errorflag in SDK MCP tool results is silently discarded.call_toolhandler increate_sdk_mcp_serveronly extractscontentfrom tool return values, discarding theis_errorflag"is_error": Trueas a supported return valueCallToolResult(isError=False)Fix: When
is_errorisTrue, raiseValueErrorwith the error text. The MCP decorator catches it and wraps inCallToolResult(isError=True)— matching the existing exception-based error path already tested intest_error_handling.Changes
src/claude_agent_sdk/__init__.py: Checkresult.get("is_error", False)after building content list; raiseValueErrorto trigger the MCP error pathtests/test_sdk_mcp_integration.py: Addtest_is_error_flagverifying both the error case (isError=Truepropagated) and success case (isErrornot set)Test plan
test_is_error_flagfails before fix (RED), passes after (GREEN)ruff checkpassesruff format --checkpassesmypy src/passes with no issues