fix: include root cause in MCPClientInitializationError message#2238
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aidandaly24 wants to merge 1 commit intostrands-agents:mainfrom
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fix: include root cause in MCPClientInitializationError message#2238aidandaly24 wants to merge 1 commit intostrands-agents:mainfrom
aidandaly24 wants to merge 1 commit intostrands-agents:mainfrom
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When MCPClient.start() fails due to a transport or auth error, the exception message was a generic "the client initialization failed" that hid the actual root cause. The original exception was preserved in the __cause__ chain but not in the string representation, making it difficult to diagnose failures in managed environments where only the error message is visible (e.g., streaming event responses). Include str(e) in the error message so the root cause is visible without needing a full stack trace. Fixes strands-agents#2237
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Description
When
MCPClient.start()fails due to a transport or auth error (e.g., OAuth token exchange failure, connection refused), theMCPClientInitializationErrorthrown contains a generic message"the client initialization failed"that hides the root cause. The original exception is preserved in__cause__(viafrom e) but not instr().In managed environments like AgentCore Harness, the error message is surfaced through a streaming event and the full stack trace is not available to the user. This makes it impossible to diagnose the root cause.
This PR includes
str(e)in the error message so the root cause is visible:Before:
MCPClientInitializationError: the client initialization failedAfter:
MCPClientInitializationError: the client initialization failed: Failed to get OAuth token for Gateway (provider=my-provider): Token has expiredThe change is at
src/strands/tools/mcp/mcp_client.pyline 223.Related Issues
Fixes #2237
Documentation PR
N/A — no documentation changes needed.
Type of Change
Bug fix
Testing
How have you tested the change?
Ran full MCP test suite: 142 passed, 0 failed
Updated
test_enter_with_initialization_exceptionto verify the root cause message is included in the errorVerified no warnings introduced in the MCP module
I ran
hatch run prepareChecklist
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