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Correct answer: A. One reports a problem with the request's structure; the other reports a problem with the work itself.
Explanation
The principle — The split is about who can act on the failure.
Why the key is correct — Protocol Errors indicate issues with the request structure itself that models are less likely to be able to fix: an unknown tool, a malformed request, a server error. Tool Execution Errors contain actionable feedback that language models can use to self-correct and retry with adjusted parameters: API failures, input validation errors, business logic errors.
Why the others are wrong — The two are reported differently, validation belongs with execution errors, and the containers are the reverse of that option.
Remember this — Structure versus work: that is the whole distinction.
Sources — MCP first-party documentation.
Sources
“Protocol Errors indicate issues with the request structure itself that models are less likely to be able to fix:”
“Tool Execution Errors contain actionable feedback that language models can use to self-correct and retry with adjusted parameters:”
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