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Defined in: server/FastMCP.ts:274 Behavioral hints for a tool (MCP 2025-03-26). Advisory only — clients may use them for UI/UX and safety decisions (e.g. auto-approving a read-only call); the server does not enforce them. Per the MCP spec, annotations from an untrusted server should not be relied upon.

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Properties

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destructiveHint?

Defined in: server/FastMCP.ts:280 The tool may perform destructive updates. Only meaningful when readOnlyHint is false. Default: true.

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idempotentHint?

Defined in: server/FastMCP.ts:282 Repeated calls with the same arguments have no additional effect. Only meaningful when readOnlyHint is false. Default: false.

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openWorldHint?

Defined in: server/FastMCP.ts:284 The tool may interact with an open world of external entities. Default: true.

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readOnlyHint?

Defined in: server/FastMCP.ts:278 The tool does not modify its environment. Default: false.

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title?

Defined in: server/FastMCP.ts:276 Human-readable title for display.