mcp: return input validation errors as tool results, not JSON-RPC errors#863
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ravyg wants to merge 2 commits intomodelcontextprotocol:mainfrom
Open
mcp: return input validation errors as tool results, not JSON-RPC errors#863ravyg wants to merge 2 commits intomodelcontextprotocol:mainfrom
ravyg wants to merge 2 commits intomodelcontextprotocol:mainfrom
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Input validation errors (missing required fields, wrong types) during tool calls are now returned as CallToolResult with IsError=true instead of JSON-RPC -32602 errors. This allows LLMs to see the validation error and self-correct, per the MCP spec. Fixes modelcontextprotocol#450
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Input validation errors (missing required fields, wrong types) during tool calls
are now returned as
CallToolResultwithIsError=trueinstead of JSON-RPC-32602errors. This allows LLMs to see the validation error and self-correct,per the MCP spec.
The existing pattern for handler-returned errors (lines 347-350 in server.go)
already converts regular errors to tool results with
IsError=true. This changeapplies the same pattern to argument schema validation and unmarshal errors,
resolving the
TODO(#450)in the code.Thanks to @iwyrkore for filing the issue and proposing the approach, and
@findleyr for the cross-SDK analysis in the discussion.
Fixes #450