Align error handling documentation with SEP-1303#967
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stephentoub merged 2 commits intomainfrom Nov 17, 2025
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- Updated McpErrorCode.InvalidParams documentation to clarify it's for protocol-level errors (malformed requests, unknown primitives) - Updated CallToolResult documentation to distinguish between tool execution errors and protocol errors - Updated McpProtocolException documentation to emphasize it's only for protocol-level errors - Added test to verify input validation errors are returned as tool execution errors (IsError=true) - Implementation already correctly handles input validation as tool execution errors per SEP-1303 Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
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[WIP] Review and implement ModelContextProtocol changes
Align error handling documentation with SEP-1303
Nov 15, 2025
stephentoub
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Nov 16, 2025
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@halter73 / @mikekistler, should we expose an option or switch somewhere to allow propagating details of arbitrary exceptions out of tools?
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I think we can defer that until there is clear signal from users that it is needed. |
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Updates documentation to reflect SEP-1303, which clarifies that input validation errors should be returned as tool execution errors (
IsError=true) rather than protocol errors, enabling language models to see error details and self-correct.Changes
McpErrorCode.InvalidParams: Clarified usage is limited to malformed requests (schema violations) and unknown primitives (tool/prompt/resource names). Explicitly excludes input validation errors.CallToolResult.IsError: Enhanced remarks to specify tool execution errors include input validation (wrong format, out of range), API failures, and business logic errors. Added examples of model self-correction scenarios.McpProtocolException: Strengthened language to emphasize protocol-level scope only, not tool execution failures.Test coverage: Added
Can_Handle_Call_Tool_Requests_With_InputValidationExceptionto verifyArgumentException(representing input validation) converts to tool execution error.Implementation Note
The SDK already implements SEP-1303 correctly. The error handler in
McpServerImpl.cs(lines 585-598) catches all exceptions exceptOperationCanceledExceptionandMcpProtocolException, converting them toCallToolResultwithIsError=true. This ensures JSON deserialization failures and parameter validation errors reach the model as actionable feedback.Original prompt
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