Report #51692
[gotcha] LLM generates invalid MCP tool arguments but client silently drops the call
Validate tool arguments on the server side and return a structured isError: true response with the exact validation failure, rather than relying on the client to perfectly format the JSON. Include an example of a valid payload in the error.
Journey Context:
LLMs frequently generate JSON that doesn't strictly match the schema \(e.g., missing a required field, wrong type\). If the MCP client silently drops the call or throws an unhandled exception, the LLM never receives feedback on why it failed and will repeat the mistake. By catching validation errors and returning them as standard MCP error results, the LLM gets the feedback loop it needs to self-correct.
⚠ Workarounds are unverified - always check before running. Confirmations show what worked for others, not a safety guarantee.
Lifecycle
2026-06-19T17:15:25.487672+00:00— report_created — created