Add option to skip output validation for mcp client #2626

Activity

1. ernestprovo23 commented on May 22, 2026

   

   ernestprovo23

   on May 22, 2026

   More actions

   hey @germanbecker, would the right shape here be a validate_structured_output: bool = True kwarg on ClientSession.__init__? that's a one-flag gate at session.py:319-320 (only validation call site i can find), default true so nothing breaks for existing users.

   noticed #1189 went down this road last fall and got closed over the safety-vs-flexibility tradeoff. the difference this time is the framing... real-world driver is servers shipping buggy output schemas that are otherwise functional, not a perf concern. happy to take it on if a maintainer (cc @felixweinberger) thinks the use case clears the bar. if not, totally fine to close.
2. germanbecker commented on May 23, 2026

   

   germanbecker

   on May 23, 2026

   Author

   More actions

   Hey! Thanks for looking into this! yes I think either at the __init__ level or at the call_tool would work. As for the justification, my example is a tool where the schema has a list of literals for an output, but it appears the maintainers forgot one possible literal. Since this will eventually be a text stream sent to an LLM, in some applications (like my case) is better so send the output that doesn't conform to schema than send an empty error
3. germanbecker commented on May 23, 2026

   

   germanbecker

   on May 23, 2026

   Last edited by germanbecker

   Author

   More actions

   For reference the current workaround:

   class MyClientSession(ClientSession):
       async def _validate_tool_result(self, name: str, result: CallToolResult) -> None:
           pass
4. maxisbey

   added

   triageQueued for automated analysis — bot will process and remove this labelQueued for automated analysis — bot will process and remove this label

   on May 31, 2026
5. ghost added

   enhancementRequest for a new feature that's not currently supportedRequest for a new feature that's not currently supported

   on Jun 1, 2026
6. ghost added

   needs decisionIssue is actionable, needs maintainer decision on whether to implementIssue is actionable, needs maintainer decision on whether to implement

   on Jun 1, 2026
7. ghost added

   P3Nice to haves, rare edge casesNice to haves, rare edge cases

   on Jun 1, 2026
8. ghost removed

   triageQueued for automated analysis — bot will process and remove this labelQueued for automated analysis — bot will process and remove this label

   on Jun 1, 2026