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Interview question · Agent, Tool & MCP Security

What is MCP tool poisoning, and how do you defend against it?

Distinguish metadata review from runtime authorization. Work through an uncalled tool, a changed definition and a server whose behavior changes without new metadata.

mediumEssentialNewUpdated Nov 2026

Distinguish metadata review from runtime authorization. Work through an uncalled tool, a changed definition and a server whose behavior changes without new metadata.

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What would you say before reading the answer?

  1. 01 State the assumptions your answer depends on.
  2. 02 Explain the mechanism and choose a control.
  3. 03 Name a condition that would change your decision.

The worked answer includes an approach, scoring criteria and follow-up questions. Compare the reasoning with your own.

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What if · the follow-ups in this answer

The answer works through 5 follow-ups like an interviewer would

A host approves a formatter's metadata and exposes it beside a mail tool. The team claims that hashing definitions and giving tools unique names prevents poisoning.

  1. What if the formatter is never called?
  2. What if the definition stays fixed while the service changes its result?
  3. What if the recipient changes after a person approves the draft?
  4. What if suspicious metadata was already loaded when the server was disabled?
  5. What would you measure in a defensive evaluation?

Each rung has a nudge, a model answer, the principle that carries over and the weak answer to avoid. Sign in free to open it.

UP NEXT ON YOUR JOURNEY
Next in this trackDesign human approval for agent actions that does not turn into rubber-stamping.Next in this trackWhen should an agent act automatically, ask for approval or refuse?Next in this trackHow do you stop injected instructions from persisting through agent memory or long-term state?
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